Part 46

Near the fallen turret, use the Hornet gun's alt-fire to destroy two wooden crates and shove a metal crate. This reveals two headcrabs; kill them with Hornets.

Look down the canals labeled "WEST" and use the Hornet gun's alt-fire to kill the barnacles.

Push the metal crate into either canal, then push it up to the fence under the "WEST" sign. Use the crate to climb over the fence.

Check under both dead barnacles for health and armor.

Move to where you can exit the water, killing the nearby headcrab with the Hornet gun before doing so.

Around the corner past the headcrab, you will find a large pool containing an ichthyosaur.

Fire Hornets into the pool continuously until the ichthyosaur stops yelling or moaning in pain for a while.

Warning: Quicksave your game. Dive into the pool to check if the ichthyosaur is dead. If not, quickrestore and fire more Hornets.

After the ichthyosaur is dead, swim to the back of the pool to find two sets of hand grenades on the floor near the fence.

Tripmine Shortcut: Quicksave. Set a tripmine at about water level on the wall next to the left end of the pool's back fence. Jump onto the tripmine, then onto the fence. Edge along the fence carefully until you can drop into the water on the other side. (Note: In earlier versions, this may require two tripmines, one below water level and one above.)

Regular Way (for Source version players and secret area): Go down the ichthyosaur pool's side passage. After it turns right, crouch and move through the large slow-moving cogwheel. Go under the double pipes and between the next two pipes. Turn right just past them and jump onto the small ledge.

Bash the padlock on the door with the crowbar. Check the room past it for a health pack and an HEV (Hazardous Environment suit) station.

Go back to the ledge and jump onto the set of steam pipes to the right. Move along them to jump past the left side of the nearby barnacle.

While avoiding leeches, crouch-walk past the next large cogwheel on either side, or time your movement under it.

While on the surface of the water, use the RPG to destroy the turret near the sandbag wall. Get onto the floor on the right side of the wall.

Crouch-jump onto the wall, then edge over to use the Hornet gun to shoot the marine standing to the right of the ladder.

Restock on RPG rockets before climbing the ladder.

At the ladder top, turn right and fire Hornets at the opening between two huge rocks until they stop swerving. This kills the two marines hiding behind them. (SRC: You may need to get off the ladder and crouch-walk slowly toward the rock gap for a better position.)

The tank behind the left rock is still alive. Get off the ladder and slowly strafe left to see the tank's turret without being seen.

Use RPG rockets to destroy the tank's turret. Then, go back down the ladder to resupply.

After the tank is destroyed, look for hand grenades in a dark niche slightly to the right of it.

Crouch-walk along the tank's right side (your left). Jump over a short obstruction.

Move up to the partly open door. Get out your pistol and sneak-shoot the turret just past the door on the left.

Use the first aid station on the opposite wall if needed.

To get to section c3a1b, use the button on the back wall to summon an elevator. Get in and use its button to start it.

From the elevator, move forward and jump over the two narrow streams of green toxic goo. Careful crouch-jumps work best. (SRC: A regular jump might be needed for the second stream.)

Turn right past the second green stream and go to the wall next to a green pool. Look past the pool to see the bottom of stairs and part of a railing.

Position yourself to barely see the marine next to the railing and fire an RPG rocket at him, hopefully killing him. (SRC: Use alt-fire Hornets instead.)

Switch to the assault rifle and shoot the other marine if he comes down the stairs. If not, crouch-walk over and sneak-shoot him with the Hornet gun.

Pick up the dropped weapons. Go up the stairs and into the large repair bay.

Wait out of sight for the marines and alien grunts to finish fighting.

Crouch-walk slowly to see into the bay. Use the Hornet gun to take down any survivors. They cannot see or shoot through the metal walkway, so if you shoot one and he runs, quickly crouch and back up where he can't see you but you can see him through the walkway. Keep firing Hornets over the walkway. (SRC: They can see and shoot through the walkway, so stay farther back while using Hornets.)

After the bay is clear, drop to its floor and bash all wooden crates for supplies, including tripmines.

Fire the tank's cannon to de...