At the start, go straight and kill anything in the room. The civilians here make for good food. Turn right and drop down the shaft. There is an android here, so kill it. Go straight through the passages until you get to the lift. There are two things to do here. Either hurry and climb up it, or if you miss it will get stuck. You'll notice one of the cargo boxes blocks the path. Crawl up around and go past the cargo box, and continue up the shaft. Go across the walkway, killing anyone up here. On the left you'll notice a door and a panel. Go ahead and break the panel, sometimes a cowardly civilian likes to hide in there. Free food. Continue on and drop down the shaft. Break the grate and drop into the elevator. Go out and follow the corridor, breaking the glass and jumping through. A message will play. While it's doing that, break the computer on the right to open the door later on. Once the message finishes the door at the end will open. Kill whomever's inside and walk through. On the left will be an opening you destroyed the computer). Drop down and destroy the eight power boxes (four on each side). That will open a door to the right of where you dropped down. Go through the door, and at the far left will be an air duct. Climb into it. When you reach the end, break the grate but DO NOT JUMP DOWN. Across from you is another air duct. There is a turret below, so instead of climbing across, use a crouch assisted leap. You should make it with minor, if any, damage. Follow that air duct to the end, and climb to your right a bit. Drop down, take out the marine and the turrets. Then destroy the eight power boxes to disable the large fans. Both large fans take you to the same place, so follow either one. They are on the ceiling down the hall either way. Climb through either and you'll be in a room with three fans (the two you can enter from and the one on the ceiling). Go through the fan on the ceiling. At the end you'll be in another room. Go through the fan on the right side and follow that tunnel until it gets to another grate. Destroy that, drop down and kill anyone in the room. Go to the opposite side of the room and break the grate on the ceiling. Climb through that and follow the series of tunnels until you get to another grate. Break it and drop down and go to the other end of the room. Break the grate there and run through the next air duct, breaking the grates at the end. Turn right and destroy the four power boxes. Turn around to face away from the destroyed power boxes, break the glass. You'll notice only one fan is slowing down. Take that fan, the one to your left, and climb through the tunnel to the end. You're at the top of a large room. Either climb or drop down and go through the tunnel on the opposite side, near the floor. Follow it to the end and turn right. At the end of the room turn left and into another tunnel. When you get out, turn to the right and destroy the two power boxes. Take the fan on the right and drop down. Look on the walls for a grate. If you to the fan on the right and face that direction, it will be the first one on your right. Climb up and destroy the grate, and crawl inside. When you get to the end you'll see a box attaches to the ceiling begin moving. Quickly climb across the ceiling and land on the box, it will protect you from the twin turrets below. Once the box is stopped walk to the other end and drop down. Take out the two turrets from behind. Turn right and climb into the opening. Turn right again, and go through the door. You'll get a message saying the humans are being attacked, and the lights will go red. Your first Predator attack. Go straight ahead, break the glass, and go through. A predator will come out of the elevator. Give it a full powered tail whip, then bite off his head as he's crouching. (This will give you the cheat if you need it also.) Climb up the shaft and you'll see a marine and a Predator fighting. Let the Predator kill the marine, then kill him with the same tactic you used before. Go to the end, turn left, get to the eggs and end the level