Unfortunately, I have never discovered a code to open it so I am not sure if there actually is something on the other side (you pass the other side of this door further on - PinothyJ). You'll come to a room with a round 'tank' (or some such) in the middle, and beyond that a larger room with three pumps (or something along those lines) in it to the south you can find a small room with a locked door and a keypad next to it (this is keypad door #1 on the map). You'll soon come to a small room with a pool and a shaft in it proceed through, going west and then north. When you move forward to the north, you'll see a partially shut door in front of you - you can't go through, so head west, down the ramp, and into the hallway going north. You're likely to come upon a number of metal and wooden boxes, so be sure to break them to find goodies.
Your starting point is on the top floor, at the southern part of the facility.
