Part 19

From the broken walkway, crouch-drop to the floor below. Break open two crates to find a tripmine and your first AR grenades.

Proceed down the hallway, ready your assault rifle for a vortigaunt. Dodge its fire if necessary.

As rubble falls due to a gargantua stomp, move slowly towards the spot. Look up for a headcrab near a ceiling hole and shoot it with your pistol, or use a hand grenade.

Two more headcrabs will drop ahead; shoot them with your pistol.

Enter section c2a1b: BIG SHAFT AND MARINE CAMP. In the room with explosives and vortigaunts, strafe so they blow themselves up.

Use the door-opening wheel to open nearby doors. If the sound persists, quicksave and quickrestore.

Climb the first ladder, turn left, and move halfway to the next ladder. Look up to spot a marine on the walkway above. Use the .357 to sneak-shoot him. If he escapes, try shooting from the base of the next ladder or finish him later.

Enter the side room where a bullsquid is dragging a dead marine. Grab both pairs of AR grenades (total six).

Climb to the top walkway and crouch-walk to the marines' area entrance. Prepare for one marine and a turret.

The turret is to the left. Crouch-strafe to the right until you can shoot one of its legs with your pistol.

After the turret is down, use the .357 to sneak-shoot the marine near the first aid station. If he moves, shoot him again quickly or crouch-walk after him.

Bash boxes and tables for ammo, including a crossbow clip.

Head down the corridor to section c2a1a: MARINE HQ AND POWER GENERATOR.

Round the corner and see explosive crates ahead; do not destroy them yet.

Edge forward with your pistol. More explosive crates are near a sandbag wall with a marine. Shoot the crates to blow them up without being seen. If other marines appear, stay hidden or let them come to you for shotgun blasts.

Note the underground bunker room with a first aid station and hand grenades.

Past the sandbag wall, find a spare tripmine on the floor near a ramp base.

(Optional Shortcut): Jump over the railing and land on a fan below. Strafe to avoid being blown back. Ride the lift up, make a run for the exit using AR grenades, and return to the room where vortigaunts blew themselves up. This is not advised but is an option.

(Recommended Path): Get out the .357 and quicksave. Back onto the first ramp, facing a red-railed balcony. A marine will appear; kill him with a headshot or two quick body shots.

Listen for an explosion, indicating another marine tripped a tripmine. If both events occur, quicksave. Otherwise, quickrestore and retry.

Crouch-walk up the ramps. Set a tripmine to the right of the doorway.

Crouch near the tripmine, turn on your flashlight, and look through the doorway. Shoot the vent grating on the ceiling twice with the pistol to let headcrabs drop.

Immediately run to the bottom of the top ramp and crouch with your shotgun ready.