Quake II/Installation

Lowering the bridge
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 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 has a broken bridge leading to the unit exit, but cannot be used yet. Instead, you will have to go into the sewer to reach the ../Comm Center/.

While it may appear that the gap leading to the exit is jumpable, a special trigger prevents you from reaching the other side; it will simply bounce you off.

Returning to Installation
Once you return from the Comm Center, you can approach the switch to lower it. 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) If you approach the raised bridge and jump into the water, you will find a cracked wall.  Shoot it to reveal a shotgun.
 * 2) In the final room, look for a staircase leading down.  Turn right and search the lower area for the double-barrel shotgun.