Part 15

Jump-crouch onto a hatch and crouch-walk onto a pipe. Jump to an adjacent pipe, run along it to a turn, and jump to a railed platform to avoid bullsquid spit.

Collect health packs and armor batteries if needed. Enter a large room with toxic water. Cross the room by jumping from a long pipe to a slanty pipe, then onto a machine next to a lift.

Crouch-walk onto the lift and use its button panel to activate it. Remain crouched until section c1a4b loads to avoid bullsquid spit.

(Optional) To access health packs and armor batteries, kill two bullsquids. Move along the rounded, slanty surface connecting the table's ledge to the lift machine, facing away from the water and using forward and strafing keys. Return to the long pipe.

After the lift stops in section c1a4b, crouch-walk forward until a bullsquid is visible. Shoot the explosive next to it to kill the bullsquid.

Proceed onto a long, curving walkway and kill approaching houndeyes with a shotgun or crowbar.

Move along the walkway to a point where you can shoot explosives between a houndeye and the walkway. This destroys part of the walkway, creating a gap.

Before jumping the gap, shoot explosives to the right to kill another houndeye. Collect health packs nearby.

Shoot two headcrabs on the other side of the gap while positioned to avoid distant bullsquid spit.

(Optional) Shoot the distant bullsquid with a pistol now, or wait for a better opportunity.

Quicksave, then take a running jump across the walkway gap. Enter the small room with a red switch between doors.

Use the shotgun, then activate the switch to proceed to section c1a4i.

In section c1a4i, as the door opens, double-barrel the zombie behind it.

Past a dying scientist, look for a barnacle tongue. To access a secret area, move into the tongue while passing the scientist, then lean backward after whacking the barnacle with a crowbar. Quicksave before attempting this.

If successful, use the first aid and HEV stations in the secret area. This area is one-visit only.

To leave the secret area without health damage, jump to the wall corner past the barnacle and hold forward, or tap the key repeatedly until you drop onto the walkway.

Move on and use the red switch next to the door to enter the rocket firing control room. Stay back as tentacle monsters grab a scientist in the firing chamber.

Leave the control room through the other door. Look up to find and kill a barnacle near a ladder (use your flashlight).

Climb the ladder and enter the room with explosive boxes and grenades. Wait for the tentacles in the firing chamber to settle down after a security guard is killed.

Crouch-walk through the firing chamber doorway and turn left. Stop near the platform edge and look down to see wooden crates blocking a ladder top.

Quicksave, then toss a grenade near the crates to destroy them. Immediately crouch-drop onto the walkway below.

As soon as you land, start crouch-walking in either direction to avoid tentacles that may have heard you. Wait for them to settle down.

Crouch-walk to the top of the ladder. Quicksave again.

Look down at the walkway below and find a boarded-over doorway. Toss a grenade at the doorway, then hurry down the ladder as it explodes.

Crouch-walk away from the ladder in case the tentacles heard you. When safe, crouch-walk through the de-boarded doorway.

Quicksave upon entering the new area.