Part 15

Jump-crouch onto the open hatch, then crouch-walk onto the pipe.

Jump to the adjacent pipe on the same level.

Run along the pipe to the right turn, then jump to the nearby railed platform, moving quickly to avoid bullsquid spit damage.

If needed, pick up health packs and armor batteries (HUD (heads-up display — the on-screen icons showing health, ammo and the minimap) elements showing player health and shields) from the table.

Enter the large room full of toxic green water.

Get on the long pipe crossing the room, then jump to the slanty pipe.

Get onto the machine next to the lift, then jump onto the lift.

Crouch-walk to the lift's button panel and use it to start the lift.

Stay crouched until section c1a4b loads to avoid bullsquid spit.

(Optional) To access a small table with health packs and armor batteries: kill both bullsquids, get on the lift, face the button panel, turn right, and look along the wall for the table. Move along the rounded, slanty surface connecting the table's ledge with the machine next to the lift, facing away from the green water and leaning forward while strafing. On the return, get off on the long pipe, not the machine.

After the lift stops in section c1a4b, crouch-walk forward until you see a bullsquid tail.

Use the pistol to shoot the explosive next to the bullsquid, killing it.

Proceed onto the long, curving walkway and kill the houndeyes (small, dog-like creatures) that approach. The shotgun is recommended over the crowbar for safety.

Move along the walkway until you can shoot explosives near another houndeye.

The explosion will destroy part of the walkway; jump the gap.

Before jumping, look to the right of the gap for more explosives to shoot, killing another houndeye.

Check the area near the explosives for health packs.

Shoot the two headcrabs (small, crab-like monsters) on the other side of the gap while positioned so a distant bullsquid cannot spit on you.

You can shoot the distant bullsquid now with the pistol, but a better opportunity will arise later.

Quicksave (save your progress).

Take a running jump across the walkway gap.

Enter the small room with a big red switch between doors.

Get out the shotgun and use the switch to proceed to section c1a4i.

As soon as the door to the right of the switch opens in section c1a4i, double-barrel the zombie (reanimated corpse) behind it.

After encountering a dying scientist (NPC (non-player character — anyone the game controls, not you) - Non-Player Character), look for a barnacle tongue hanging down.

(Optional Secret Area) To access a secret area: move into the barnacle tongue while passing the scientist, then lean backward immediately after whacking the barnacle with the crowbar. Quicksave before attempting this, as it's easy to miss. Inside, you'll find first aid and HEV (Hazardous Environment) stations. This is a one-visit-only secret area.

To avoid health damage when leaving the secret area: jump to the wall corner past the barnacle and hold forward. If you don't slide down, tap forward repeatedly until you drop onto the walkway.

Move on and open the next door using the red switch next to it.

Past the door is the rocket firing control room. Stand back as one of the three tentacle monsters in the rocket firing chamber grabs a scientist. The tentacles will not attack you in the control room.

Leave the control room through the other door.

Look up to kill a barnacle near a ladder, using your flashlight to see it on the ceiling.

Climb the ladder and enter the room with explosive boxes and hand grenades.

A security guard will run into the firing chamber and be killed by the tentacles; wait for them to settle down.

Crouch-walk through the firing chamber doorway and turn left.

Near the edge of the platform, stop and look down to see a ladder top blocked by wooden crates.

Quicksave.

Toss a grenade to land near the crates and destroy them.

The instant the grenade explodes, crouch-drop off your platform onto the walkway below.

As soon as you land, start crouch-walking in either direction to avoid the tentacles, which may attack the spot where you landed.

If hit, quickrestore (load your last save) and try again.

Wait until the tentacles settle down, then crouch-walk to the top of the ladder.

Quicksave again.

Look down at the walkway below to find a boarded-over doorway.

Toss a grenade at the boarded-over doorway.

Hurry down the ladder as soon as the grenade explodes.

As before, crouch-walk away in case the tentacles heard you.

When safe, crouch-walk to the de-boarded doorway and go through it.

Quicksave again upon entering the new area.