Part 19

Crouch-drop down to the floor below the broken walkway, breaking crates to find a tripmine and assault rifle (AR) grenades.

Proceed down the hallway, ready your assault rifle for a vortigaunt, and strafe to dodge its fire.

As rubble falls ahead due to a gargantua stomp, move slowly towards it with your flashlight on. Sneak-shoot a headcrab near a ceiling hole or use a hand grenade.

Past that, two more headcrabs will drop; shoot them and move to section c2a1b.

In the next room, strafe to let vortigaunts blow themselves up. Use the door-opening wheel to open the nearby doors.

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

Enter the side room, grab both pairs of AR grenades (totaling six).

Climb the ladder to the top walkway and crouch-walk to the marines' area.

Take down the turret by crouch-strafing to shoot one of its legs.

Get out the .357 and sneak to shoot the marine near the first aid station. If he moves, pursue and shoot him again.

Bash boxes and tables for ammo, including a crossbow clip. Head down the corridor to section c2a1a.

When rounding the next corner, note the explosive crates ahead.

Edge forward with your pistol and shoot the explosive crates next to a sandbag wall to blow them up, luring two other marines. Stay hidden or let them come for shotgun blasts.

In the underground bunker-style room near the sandbag wall, find a first aid station and hand grenades.

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

Optional Shortcut: Jump over the railing onto a moving fan below, then take the power-restoring steps and ride the lift up. This allows a quick run for the exit using AR grenades, but you won't be safe until returning to the room with the self-detonating vortigaunts.

Recommended Path: Get out the .357 and quicksave. Back onto the first ramp, face the red-railed balcony. Kill the marine that appears there before he escapes.

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

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

Crouching 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.