Quake II/Installation

Lowering the drawbridge
Installation is the second map in the game, and the first one you will revisit.

When the elevator door opens and you advance into the room, you will encounter Strogg guards hiding behind a few crates, as well as a few on the floor above. Proceed through the doorway ahead and turn left. The Machine Gun (~ "Machinegun") can be collected here.

In the next room, take the elevator to the second floor. You can head left to collect some ammo (and armor), or right to the outside area. This area had a bridge leading to the unit exit, but it got blasted just before you reached it. It is possible to run-jump across the gap where the bridge was and kill a few guards lurking in the hallway beyond, but further progress is blocked by a raised drawbridge. To reach the lever that lowers the drawbridge, you will have to go into the sewer to reach the ../Comm Center/.

Returning to Installation
Once you return from the Comm Center by another route, you can throw the lever to lower the drawbridge. This allows you to cross the bridge, and reach the exit in the final room. Just before you enter the elevator, a message will state that this is the end of the unit; if you didn't collect everything desired, this will be your last chance to do so.

After exiting the unit, you will continue in the ../Ammo Depot/.

Secrets

 * 1) Before entering the large, round sewer opening, go into a smaller rectangular opening to the left of it and stay near the right wall.  Watch for a crack in the wall.  Shoot it to open a hidden chamber and reveal a Shotgun.
 * 2) In the final room, look for a staircase leading down.  Search the lower area for a Super Shotgun.