Continue down the corridor, making sure to take
advantage of the health recharger on the wall. As you enter the doorway,
you'll hear a woman cry for help. To your left will be two combine
police beating on someone. They'll see you and go after you. They are
both easily taken care of with the crowbar when you get close; make sure
to hit them in the head for an easy takedown. You can then pick up the
pistol one of them drops; your first gun! The woman says you best run,
so take her advice and smash your way through the next doorway.
Go up the stairs, taking out the entire combine that comes down after you. At the top you will be outside again, this time next to a railway track. Take a moment to take in the scenery, then head left. There will be another set of stairs down to the tracks. Go down, and then go back up as the train approaches. Wait for the train to stop, then jump on top and use it to get across (there's a ladder on the other side to your right that you can climb up). Once here, some combine police will show up back where you came out; they are easily taken out via the explosive barrels dotted around them. Go left and duck inside the house.
There's a scanner here; little more than a nuisance, but take care of it anyway. Go into the room on the right and clear the doorway by either picking up the objects and moving them, or shooting the barrels nearby. More combine will have appeared at the starting point, so be careful. You will now be behind the house, with a fence on your left. Some combine will appear on the level above you; shoot the barrels nearby to dispose of them. Go through the fence and around the house, then jump over the broken fence here back to the front. Sprint right to avoid the combine shooting at you, then duck into the open vent with a lambda symbol on top of it (this symbol denotes an area with supplies, so look out for it).
Pick up the items, and then smash your way through the vent cover. Some combine will appear on the opposite side of the track again; kill them if you want. Go right, and drop down onto the track (using the piece of wood to break your fall). Head right. A combine will appear from the right; shoot the barrel near him, but avoid the other barrel that will roll towards you. There will be some stairs up here, with a combine pushing a flaming barrel towards you. Shoot the barrel quickly and you'll have taken care of both problems.
Go up the stairs, and another combine will appear from around a corner. Shoot the barrel near him for another fun kill, or just get rid of him the old fashioned way. Yet another combine will come down some steps, with yet another conveniently placed explosive barrel next to him. Continue up the stairs, and you'll end up above the tracks on a walkway. There will be combine below shooting at you; quickly smash the boxes in your way with the crowbar to avoid getting hit (as well as conserving ammo). Get down these stairs, and drop onto the tracks again. There's a health recharger on the wall opposite you, to use it if you need to.
Head out of the tunnel and quickly turn right, through the opening in the fence and onto the walkway. Don't bother trying to get through the door, it won't open. Instead sit back and relax as a train mows down the entire combine left chasing you. Once you're ready to move on, jump down into the canal. Head downstream; ignoring the scanners above (they can't see you). You'll come to a train carriage blocking the way, with a ladder on the left side. Go up the ladder and drop into the carriage. After a small conversation with a civilian and a Vortigaunt (he won't hurt you, they're friendly in this game), you'll be let out.
Smash your way through the debris, and stop once you see a bird take off. It'll be gobbled up by a barnacle hanging off the ceiling. Use this chance to get past it while it's busy, and keep zigzagging your way through the debris. You'll eventually hear gunshots and see some civilians running into a tunnel. One civilian will shout to you from a grating on the right; go towards him and he'll be shot. Take out the combine that got him from behind, then any that appear from behind you. Be careful when going around the corner, as there's a combine with a mounted gun. Quickly sprint and duck into a large pipe in the wall on your right (there will be some boxes to act as a quick piece of cover from the gunfire). Once inside, take care of the combine that appear and go left down the tunnel.
You will now be in a secret outpost of sorts for the Underground Railroad. Grab any supplies you can, listen to the radio message (what are manhacks? well...), and then go up the ladder. Poke your head over out of the hole, and shoot the explosive barrel nearby (remember to duck and cover to avoid the explosion). This will take care of the two combine sitting next to the mounted machinegun from before. A lot of combine and scanners will now appear from below and above you, so take up that machine gun and get rid of them (take advantage of the barrels thrown about the place, and try to shoot out whatever the combine are standing on if they're above you)). Eventually a combine APC will appear on the road to your right, and cause loads of barrels to fall beside you. There is a path to your right as well blow the road; shoot out the explosive barrel there to create a path across the gap, and then sprint down. The APC will start shooting rockets at the gun placement, and with all those barrels around, you'd best want to go somewhere else.
You'll end up in yet another tunnel; there are some supplies near the lambda symbol to your left if you want them. Keep going, making your way around the barnacles (or just shooting them with your pistol) and debris. On the other side, you'll see the APC drive away out of sight. Go around to your left, and after the small conversation from one of the surviving citizens, make your way through the nearby pipe. In this next room, there are combine above you, who will see you if you try to keep going. They will run off regardless, so don't bother wasting ammo on them just yet. Go through the next pipe, and jump into the water. The same combine will now chuck explosive barrels down to you. One will be on fire, so duck under the water to avoid the blasts. They will now shoot at you' take your pistol out and aim for the head. The blast will have created a hole in the next pipe, so keep going.
On the other side, there will be some combine jumping down from a higher level to get to you. Quickly shoot the barrel near them to get rid of them. Use the debris around this area as cover against the combine going straight at you. To the right, there will be another combine jumping down at you. Quickly pick up the explosive barrel near you, throw it near here he will land, and blow it up. Once this happens, loads of combine will appear on the wooden bridge nearby. Don't bother shooting them; shoot the barrels at the base of the bridge. Aren't the laws of physics fun? After you've picked your jaw off the floor, take care of the combine jumping down behind the bridge; try shooting them before they land, as they don't bother to shoot back until they're grounded. There will be some barrels up a ramp; go up and push one of them down the next ramp. It will slide into a barnacle. Use the remaining barrels to get past it quickly.
There will be another ramp here; throw an explosive barrel down the ramp, and let a barnacle catch it. Shoot it until it's on fire, so as to delay the explosion until it's right on top of the barnacle. His will single-handedly get rid of every barnacle in this area, so simply stroll by collecting the supplies. Up this next ramp, you'll emerge in a small canal; an explosive barrel will drop down, so either shoot it or wait for it to explode before diving in. Now, more barrels will drop down. Simply duck underwater until they're gone, and then shoot any combine attacking you from above.
Now before you keep going, try to take pot shots at any barrels you see on the higher level (not including ones stood upright); these barrels are supposed to roll down and catch you unawares, so get rid of as many as possible now so you don't have to deal with them. Continue down the canal; go up the ladder and over the fence. More barrels will appear now, so get underwater again and go to the opposite end of the canal. Again, shoot any and all barrels and combine you see here, using the conveniently placed cover nearby. Once it seems clear, start running down the stretches of wood, going around and jumping through the broken grating. There will be some barrels that you couldn't see being dropped down, so just keep moving.
Once through, you'll have your first physics puzzle to deal with! This is easy; simply pick up any and all bricks and place them on the left side of the seesaw, until it's turned into a handy ramp for you to run up. Once over the gap, continue down the tunnel and a helicopter will spot you (surprisingly enough). You will have to drop down a slippery slope and into a drained canal, where the helicopter will now start to shoot at you. The objective here is to use as much cover as possible, dancing in between them when the helicopter stops shooting. Keep going down the left, avoiding the barnacle, and into the door, using cover as much as possible. Once inside, go down the nearby ladder and pick up the supplies, then come back up and keep going down the corridor.
Pick up the supplies around this area (there are some health packs to the left, just crouch down the narrow passageway to get to them), then go right. There will be another slop with barnacles here (ignore the helicopter, it can't get to you). Use the same strategy here as before; pick up the nearby explosive barrel, and throw it down the slope, then shoot it twice when they latch onto it. This will kill the first line of barnacles, and the other line should latch onto the debris that's created (this second line doesn't need to be killed, but if you must, there is another barrel in the narrow passageway with the health packs). Go down the slope and through the doorway to your left. You'll come across another slope; same strategy here. You will eventually appear outside again; avoid the helicopter by sprinting to your left. Follow the corridor around, grabbing supplies as you go.
Eventually you'll come across a small outpost with one person waiting there for you. Don't rest up yet though, as manhacks will soon burst through the wooden door. The easiest way to take care of them is to use your crowbar; don't try to shoot them; it's just a waste of ammo since they're so hard to hit. Once they're gone, grab the supplies from the higher level and keep going. Behind the next door will be more manhacks, so be ready for them. Be careful around this next corner, as there will be a corridor full of barrels and manhacks. One will ignite, so quickly run back and wait for them all to explode, killing any manhacks that get past. Keep going, past the door that leads outside, and barb the supplies here. Go back and through the door you passed. Quickly run for the opposite door, move the barrel and go through. Close it behind you before the manhacks can get to you.
Leave the explosive barrel here, you'll need it. Jump onto the pipe and into the vent. Go through, killing the manhack that meets you inside, and into the next room. There's a bunch of supply boxes here, so take advantage of the situation. Go back, and before leaving the vent, shoot the barrel from before, killing the combine that appears. Go down the ladder, and a combine will jump down from above with an SMG. Quickly shoot the barrel behind him and pick it up. Two more combine will appear on the far end of this corridor; use the pistol here, as the SMG isn't suited for long-range. Turn around and you'll see a barrel; don't shoot it, just gently throw it aside into the water. Go inside, and head right for the end. A zombie will burst through the box and crawl towards you' quickly shoot it dead. Pick up the supplies (including your first grenade), then go back. Another combine will now jump down after you. Just shoot the barrel you left behind to get rid of him. Get out, and then keep heading forward.
Sprint then jump onto the pipes to the right of you, then jump onto the middle of the rotating...thing? Meh. Regardless, once you're on the middle of it, jump down and swim into the hole at the bottom of the left-hand wall. There will be a small air pocket for you to catch your breath if you want. Keep going and you'll emerge in yet another tunnel. Go left, and kill the combine that drop down. Don't bother going any further forward; it's a dead end, and all it does it spawn more combine and manhacks. Instead, shoot the barnacle above the stairs to your left, then go up. Get rid of the barrel and jump onto the big pipe in the middle. Go right, avoiding the steam jets. In this next room, there will be an explosive barrel, and some more barnacles; do what you have to do. Keep following the pipe and you'll see a manhack on the other side of a fence. Shoot it now to get rid of it while it's at a safe distance. Break the wooden fence on you right, drops down and turn around under the pipe to get some more supplies.
Drop down into the water, go left and up the ladder. Poke your head over the top and shoot the combine you see on the higher level; this will release a bunch of explosive barrels. Shoot them as fast as you can until one blows up, or they get too close (remember to duck underwater if things get hairy). Once they're gone, go over the top and equip your SMG. Around the corner some combine will drop down to get you' easily taken care of with the SMG. In the nearby corridor, as you approach the door on the far end, some manhacks will appear. Don't go any further, instead lure the manhacks to you and take care of them. This is because once you get close to the door, even more manhacks will appear. Again, do the same here. Go through the door once they're gone, and through the dark corridor (remember your flashlight).
There is a vent here; break through and drop down to the lower level. You'll land in a room full of explosive barrels and manhacks. Don't shoot anything yet' instead, go down the ladder to your left and into the water. Once you're there, shoot the barrels from below. If any manhacks manage to get to you, they're easily taken care of as they move very slowly in the water. Once they're gone, go back up the ladder nod onto the pipe at the top of the room. Go left, crouch and land on the walkway. Go through into the next room, and around to the right of the pipes. Drop down pipe by pipe to the valve at the bottom. Use it, then go back up the ladder and back into the other room.
More manhacks will appear; again, us the water to your advantage. After they're gone, swim down to the bottom of the room and through the large pipe. Go up to the door and up the ladder, and then look down to the bottom. You should see a row of wooden planks at the bottom. Shoot each one once to release the debris from underneath them (you may have to shoot one of the boxes to release some of it). Use the debris to jump over the water onto the other side. Go through the next corridor.
Go up the ladder and drop onto the wooden planks; drop down to the lower level, then get rid of the scanner quickly. Some combine and manhacks will appear; shoot the combine quickly, then deal with the manhacks. Go down to where they appeared, and use the barrel to jump up onto the next level. In the next tunnel, some manhacks will fly through the boxes; be ready for them. Further along here, there are some barnacles guarding supplies. Use debris nearby to distract them while you grab it. Go back and through the doorway you went past. Go up the ladder and across the walkway into the next room, where you should drop down. Go through this next corridor and you'll again appear outside. Go left and down the planks, avoiding the radiation. There will be an outpost up ahead with one guy fighting some headcrabs. Help him out, pick up some supplies, listen to the radio message, and keep going.
Go under the debris, and then watch for the shell that comes down in front of you. These shells contain headcrabs, so shoot as many as you can before they burrow into the ground. When you go near them, they come out again, so use your crowbar up close to kill them. There will be one scene where you'll see what a headcrab does to you; help him out if you want. Keep going around, and you'll come to a bit with two dead zombies. They come back to life when you go near them, so just take them out from a distance (watch out as one of them throws a barrel at you). Keep going, avoiding the electrical wire, and another zombie will burst through a wall. Take him out with the crowbar, dodging his attacks. Move through this next area careful, as the walls are conducting electricity. A shell will land on the other side; see if you can lure them into the walls. Once through, continue going, making sure t kill the combine that pops up out of the water.
Follow the wooden path around and you'll come to the last station, where an airboat has been set up for you. Once the gate is opened for you, climb in and drive out. Follow the canal around, and you'll come to a closed gate. Go onto dry land and get out, then head for the gate control on the right of it. Use it to slowly open the gate until it locks into position. Get back into the boat, and drive through (make sure you hit the supply crate on the way).
Go up the stairs, taking out the entire combine that comes down after you. At the top you will be outside again, this time next to a railway track. Take a moment to take in the scenery, then head left. There will be another set of stairs down to the tracks. Go down, and then go back up as the train approaches. Wait for the train to stop, then jump on top and use it to get across (there's a ladder on the other side to your right that you can climb up). Once here, some combine police will show up back where you came out; they are easily taken out via the explosive barrels dotted around them. Go left and duck inside the house.
There's a scanner here; little more than a nuisance, but take care of it anyway. Go into the room on the right and clear the doorway by either picking up the objects and moving them, or shooting the barrels nearby. More combine will have appeared at the starting point, so be careful. You will now be behind the house, with a fence on your left. Some combine will appear on the level above you; shoot the barrels nearby to dispose of them. Go through the fence and around the house, then jump over the broken fence here back to the front. Sprint right to avoid the combine shooting at you, then duck into the open vent with a lambda symbol on top of it (this symbol denotes an area with supplies, so look out for it).
Pick up the items, and then smash your way through the vent cover. Some combine will appear on the opposite side of the track again; kill them if you want. Go right, and drop down onto the track (using the piece of wood to break your fall). Head right. A combine will appear from the right; shoot the barrel near him, but avoid the other barrel that will roll towards you. There will be some stairs up here, with a combine pushing a flaming barrel towards you. Shoot the barrel quickly and you'll have taken care of both problems.
Go up the stairs, and another combine will appear from around a corner. Shoot the barrel near him for another fun kill, or just get rid of him the old fashioned way. Yet another combine will come down some steps, with yet another conveniently placed explosive barrel next to him. Continue up the stairs, and you'll end up above the tracks on a walkway. There will be combine below shooting at you; quickly smash the boxes in your way with the crowbar to avoid getting hit (as well as conserving ammo). Get down these stairs, and drop onto the tracks again. There's a health recharger on the wall opposite you, to use it if you need to.
Head out of the tunnel and quickly turn right, through the opening in the fence and onto the walkway. Don't bother trying to get through the door, it won't open. Instead sit back and relax as a train mows down the entire combine left chasing you. Once you're ready to move on, jump down into the canal. Head downstream; ignoring the scanners above (they can't see you). You'll come to a train carriage blocking the way, with a ladder on the left side. Go up the ladder and drop into the carriage. After a small conversation with a civilian and a Vortigaunt (he won't hurt you, they're friendly in this game), you'll be let out.
Smash your way through the debris, and stop once you see a bird take off. It'll be gobbled up by a barnacle hanging off the ceiling. Use this chance to get past it while it's busy, and keep zigzagging your way through the debris. You'll eventually hear gunshots and see some civilians running into a tunnel. One civilian will shout to you from a grating on the right; go towards him and he'll be shot. Take out the combine that got him from behind, then any that appear from behind you. Be careful when going around the corner, as there's a combine with a mounted gun. Quickly sprint and duck into a large pipe in the wall on your right (there will be some boxes to act as a quick piece of cover from the gunfire). Once inside, take care of the combine that appear and go left down the tunnel.
You will now be in a secret outpost of sorts for the Underground Railroad. Grab any supplies you can, listen to the radio message (what are manhacks? well...), and then go up the ladder. Poke your head over out of the hole, and shoot the explosive barrel nearby (remember to duck and cover to avoid the explosion). This will take care of the two combine sitting next to the mounted machinegun from before. A lot of combine and scanners will now appear from below and above you, so take up that machine gun and get rid of them (take advantage of the barrels thrown about the place, and try to shoot out whatever the combine are standing on if they're above you)). Eventually a combine APC will appear on the road to your right, and cause loads of barrels to fall beside you. There is a path to your right as well blow the road; shoot out the explosive barrel there to create a path across the gap, and then sprint down. The APC will start shooting rockets at the gun placement, and with all those barrels around, you'd best want to go somewhere else.
You'll end up in yet another tunnel; there are some supplies near the lambda symbol to your left if you want them. Keep going, making your way around the barnacles (or just shooting them with your pistol) and debris. On the other side, you'll see the APC drive away out of sight. Go around to your left, and after the small conversation from one of the surviving citizens, make your way through the nearby pipe. In this next room, there are combine above you, who will see you if you try to keep going. They will run off regardless, so don't bother wasting ammo on them just yet. Go through the next pipe, and jump into the water. The same combine will now chuck explosive barrels down to you. One will be on fire, so duck under the water to avoid the blasts. They will now shoot at you' take your pistol out and aim for the head. The blast will have created a hole in the next pipe, so keep going.
On the other side, there will be some combine jumping down from a higher level to get to you. Quickly shoot the barrel near them to get rid of them. Use the debris around this area as cover against the combine going straight at you. To the right, there will be another combine jumping down at you. Quickly pick up the explosive barrel near you, throw it near here he will land, and blow it up. Once this happens, loads of combine will appear on the wooden bridge nearby. Don't bother shooting them; shoot the barrels at the base of the bridge. Aren't the laws of physics fun? After you've picked your jaw off the floor, take care of the combine jumping down behind the bridge; try shooting them before they land, as they don't bother to shoot back until they're grounded. There will be some barrels up a ramp; go up and push one of them down the next ramp. It will slide into a barnacle. Use the remaining barrels to get past it quickly.
There will be another ramp here; throw an explosive barrel down the ramp, and let a barnacle catch it. Shoot it until it's on fire, so as to delay the explosion until it's right on top of the barnacle. His will single-handedly get rid of every barnacle in this area, so simply stroll by collecting the supplies. Up this next ramp, you'll emerge in a small canal; an explosive barrel will drop down, so either shoot it or wait for it to explode before diving in. Now, more barrels will drop down. Simply duck underwater until they're gone, and then shoot any combine attacking you from above.
Now before you keep going, try to take pot shots at any barrels you see on the higher level (not including ones stood upright); these barrels are supposed to roll down and catch you unawares, so get rid of as many as possible now so you don't have to deal with them. Continue down the canal; go up the ladder and over the fence. More barrels will appear now, so get underwater again and go to the opposite end of the canal. Again, shoot any and all barrels and combine you see here, using the conveniently placed cover nearby. Once it seems clear, start running down the stretches of wood, going around and jumping through the broken grating. There will be some barrels that you couldn't see being dropped down, so just keep moving.
Once through, you'll have your first physics puzzle to deal with! This is easy; simply pick up any and all bricks and place them on the left side of the seesaw, until it's turned into a handy ramp for you to run up. Once over the gap, continue down the tunnel and a helicopter will spot you (surprisingly enough). You will have to drop down a slippery slope and into a drained canal, where the helicopter will now start to shoot at you. The objective here is to use as much cover as possible, dancing in between them when the helicopter stops shooting. Keep going down the left, avoiding the barnacle, and into the door, using cover as much as possible. Once inside, go down the nearby ladder and pick up the supplies, then come back up and keep going down the corridor.
Pick up the supplies around this area (there are some health packs to the left, just crouch down the narrow passageway to get to them), then go right. There will be another slop with barnacles here (ignore the helicopter, it can't get to you). Use the same strategy here as before; pick up the nearby explosive barrel, and throw it down the slope, then shoot it twice when they latch onto it. This will kill the first line of barnacles, and the other line should latch onto the debris that's created (this second line doesn't need to be killed, but if you must, there is another barrel in the narrow passageway with the health packs). Go down the slope and through the doorway to your left. You'll come across another slope; same strategy here. You will eventually appear outside again; avoid the helicopter by sprinting to your left. Follow the corridor around, grabbing supplies as you go.
Eventually you'll come across a small outpost with one person waiting there for you. Don't rest up yet though, as manhacks will soon burst through the wooden door. The easiest way to take care of them is to use your crowbar; don't try to shoot them; it's just a waste of ammo since they're so hard to hit. Once they're gone, grab the supplies from the higher level and keep going. Behind the next door will be more manhacks, so be ready for them. Be careful around this next corner, as there will be a corridor full of barrels and manhacks. One will ignite, so quickly run back and wait for them all to explode, killing any manhacks that get past. Keep going, past the door that leads outside, and barb the supplies here. Go back and through the door you passed. Quickly run for the opposite door, move the barrel and go through. Close it behind you before the manhacks can get to you.
Leave the explosive barrel here, you'll need it. Jump onto the pipe and into the vent. Go through, killing the manhack that meets you inside, and into the next room. There's a bunch of supply boxes here, so take advantage of the situation. Go back, and before leaving the vent, shoot the barrel from before, killing the combine that appears. Go down the ladder, and a combine will jump down from above with an SMG. Quickly shoot the barrel behind him and pick it up. Two more combine will appear on the far end of this corridor; use the pistol here, as the SMG isn't suited for long-range. Turn around and you'll see a barrel; don't shoot it, just gently throw it aside into the water. Go inside, and head right for the end. A zombie will burst through the box and crawl towards you' quickly shoot it dead. Pick up the supplies (including your first grenade), then go back. Another combine will now jump down after you. Just shoot the barrel you left behind to get rid of him. Get out, and then keep heading forward.
Sprint then jump onto the pipes to the right of you, then jump onto the middle of the rotating...thing? Meh. Regardless, once you're on the middle of it, jump down and swim into the hole at the bottom of the left-hand wall. There will be a small air pocket for you to catch your breath if you want. Keep going and you'll emerge in yet another tunnel. Go left, and kill the combine that drop down. Don't bother going any further forward; it's a dead end, and all it does it spawn more combine and manhacks. Instead, shoot the barnacle above the stairs to your left, then go up. Get rid of the barrel and jump onto the big pipe in the middle. Go right, avoiding the steam jets. In this next room, there will be an explosive barrel, and some more barnacles; do what you have to do. Keep following the pipe and you'll see a manhack on the other side of a fence. Shoot it now to get rid of it while it's at a safe distance. Break the wooden fence on you right, drops down and turn around under the pipe to get some more supplies.
Drop down into the water, go left and up the ladder. Poke your head over the top and shoot the combine you see on the higher level; this will release a bunch of explosive barrels. Shoot them as fast as you can until one blows up, or they get too close (remember to duck underwater if things get hairy). Once they're gone, go over the top and equip your SMG. Around the corner some combine will drop down to get you' easily taken care of with the SMG. In the nearby corridor, as you approach the door on the far end, some manhacks will appear. Don't go any further, instead lure the manhacks to you and take care of them. This is because once you get close to the door, even more manhacks will appear. Again, do the same here. Go through the door once they're gone, and through the dark corridor (remember your flashlight).
There is a vent here; break through and drop down to the lower level. You'll land in a room full of explosive barrels and manhacks. Don't shoot anything yet' instead, go down the ladder to your left and into the water. Once you're there, shoot the barrels from below. If any manhacks manage to get to you, they're easily taken care of as they move very slowly in the water. Once they're gone, go back up the ladder nod onto the pipe at the top of the room. Go left, crouch and land on the walkway. Go through into the next room, and around to the right of the pipes. Drop down pipe by pipe to the valve at the bottom. Use it, then go back up the ladder and back into the other room.
More manhacks will appear; again, us the water to your advantage. After they're gone, swim down to the bottom of the room and through the large pipe. Go up to the door and up the ladder, and then look down to the bottom. You should see a row of wooden planks at the bottom. Shoot each one once to release the debris from underneath them (you may have to shoot one of the boxes to release some of it). Use the debris to jump over the water onto the other side. Go through the next corridor.
Go up the ladder and drop onto the wooden planks; drop down to the lower level, then get rid of the scanner quickly. Some combine and manhacks will appear; shoot the combine quickly, then deal with the manhacks. Go down to where they appeared, and use the barrel to jump up onto the next level. In the next tunnel, some manhacks will fly through the boxes; be ready for them. Further along here, there are some barnacles guarding supplies. Use debris nearby to distract them while you grab it. Go back and through the doorway you went past. Go up the ladder and across the walkway into the next room, where you should drop down. Go through this next corridor and you'll again appear outside. Go left and down the planks, avoiding the radiation. There will be an outpost up ahead with one guy fighting some headcrabs. Help him out, pick up some supplies, listen to the radio message, and keep going.
Go under the debris, and then watch for the shell that comes down in front of you. These shells contain headcrabs, so shoot as many as you can before they burrow into the ground. When you go near them, they come out again, so use your crowbar up close to kill them. There will be one scene where you'll see what a headcrab does to you; help him out if you want. Keep going around, and you'll come to a bit with two dead zombies. They come back to life when you go near them, so just take them out from a distance (watch out as one of them throws a barrel at you). Keep going, avoiding the electrical wire, and another zombie will burst through a wall. Take him out with the crowbar, dodging his attacks. Move through this next area careful, as the walls are conducting electricity. A shell will land on the other side; see if you can lure them into the walls. Once through, continue going, making sure t kill the combine that pops up out of the water.
Follow the wooden path around and you'll come to the last station, where an airboat has been set up for you. Once the gate is opened for you, climb in and drive out. Follow the canal around, and you'll come to a closed gate. Go onto dry land and get out, then head for the gate control on the right of it. Use it to slowly open the gate until it locks into position. Get back into the boat, and drive through (make sure you hit the supply crate on the way).
