Secret Places (7)
This secret is inside the power generator (where you have to shoot down the narrow tunnel to hit the alien pawprint switch). When facing the alien switch, the secret would be directly behind you. Press on the wall to open it.
In the power generator room, one of the crevices has a secret door. Press against the only part of the wall that isn't flashing (I caught this snapshot in the split second the lights were flashing).
Upon entering the previous secret, turn left. Walk to the end of the tunnel and turn left facing the wall. Jump to find another secret.
Go to the room with the water turbines. If you walk by the security screen you'll hear a door opening somewhere. Before you can access it, you have to go underwater and hit the two switches. Upon surfacing, go back to the security screen. The hidden door is on the exact opposite side of the room from the security screen. When you hear the door opening, run to the other side to find it.
Continue from the previous room until you get to the place where you must shoot an orange switch to get any further. Shoot the switch to move the bridge and get across. Upon entering the next room, take a left. One of the corner pillars can be opened revealing armor.
Continue from the previous location. The next room will have a lot of explosions. Wait for the explosions to finish, then find the big hole in the wall. Use this hole to gain the height needed to reach the upper area of this room. The secret place is in the ventilation shaft.
After going through the ventilation shaft you'll see a babe. To the right is a crack in the wall. Blow it up to find the last secret place (the explosion will kill her).