Shadowgrounds/'The Weather Station 5'

Initial attack
After arriving at the facility, you will need to reach the command area. It is just off the central corridor that can be reached by going through two doors.

Once you reach the command center, you will need to fill up your ammo. There will be three initial waves:
 * 1) One from the south gate.
 * 2) One from the East.
 * 3) One from the north.

There is a short time between individual waves for you to defeat the enemies, as well as to move into position.

After the first three waves, you are called back to the command center. You will gain access to three sentry guns. For the best result, place two at the east gate. The third can be first places at the west gate, and then carried to the north once the wave there is defeated. After a short time (when you likely have two sentries placed), four last wave swill begin: The West gate. The East gate. The North gate. The East gate.  You will be recalled to the command center once all waves are defeated, before being send down the elevator.

Rescuing the APC
From the lower level, you will have to unlock and open the doors. Find the terminal, and head directly to the exit. There will be spider-like scavengers trying to attack you, but the enemies build up in the exit corridor.

When you head outside, follow the lights on the path as it makes the left hand turn. When you reach the APC, kill all nearby enemies to finish the level.