Part 46

Near the fallen turret, use the hornet gun's altfire to destroy two wooden crates and shove a metal crate. This reveals two headcrabs that can be killed with hornets.

Look down the canals labeled "WEST" to find barnacles; kill them with the hornet gun's altfire.

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. Before doing so, kill the nearby headcrab with hornets.

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 reacting. Quicksave, then dive in to check if it 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.

To use a tripmine shortcut: Quicksave. Set a tripmine at 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 to drop into the water on the other side. (Note: In earlier game versions, you might need two tripmines, one below water level and one above, to get onto the fence.)

To use the regular path (for the secret area and for Source version players who cannot use the tripmine shortcut): Go down the ichthyosaur pool's side passage. After it turns right, crouch and move through the large slow-moving cogwheel, then go under the double pipes and between the next two pipes.

Turn right just past the pipes and jump onto the small ledge. (This jump can be tricky.)

Bash the padlock on the door with the crowbar, then check the room past it for a health pack and an HEV station (a station that restores your suit's power).

Go back to the ledge and jump onto the 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 to go under it.

While on the water's surface, 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 to the right of the ladder.

After the marine is dead, restock on RPG rockets before climbing the ladder.

At the ladder's top, turn right and fire hornets at the opening between two huge rocks until the hornets stop swerving. This indicates the two marines hiding there are dead. (SRC: You may need to get off the ladder and crouch-walk slowly toward the rock gap for a better horneting position.)

The tank behind the left rock is still active. Get off the ladder and slowly strafe left to see the tank's turret without being seen. You can destroy the turret with altfire hornets, but RPG rockets are faster. Go back down the ladder to resupply if needed.

After the tank is destroyed, look for hand grenades in a dark niche to its right. Crouch-walk along its right side (your left).

Jump over a short obstruction, then move to the partly open door. Get out your pistol and 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, then get in and use its button to operate it.

Move forward from the elevator and jump over the two narrow streams of green toxic goo. Careful crouch-jumps usually 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.

Get to where you can barely see the marine next to the railing, then fire an RPG rocket at him, ideally killing him. (SRC: Use altfire 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, then go up the stairs and into a large repair bay.

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

Crouch-walk slowly into the bay and 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 moves, 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 you through the walkway, so stay farther back while horneting.)

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

Fire the tank's cannon to proceed.