Penumbra: Requiem/Steam

Head down the ladder, and go to the back right corner. You should see two crates - stack one on top of the other by using the ramp, then push the upper crate into the chute.

Push this crate to the other back corner of the level, placing it on any pressure plate. Find the other crate nearby, and put it on a second pressure plate. Stand on the third, and a nearby door will open.

In this small room, play the radio and note the combination. Move the crate to reveal a hatch, which contains the first key. Pick up some wood, and bring it to the boiler room.

Put the wood in the boiler, and start the ignition. Start pumps 2 and 3.

Head to the acid pit, and ride the lift up. Turn right and head straight until you see a locker. Enter the combination, and collect the chemical. (If you try bringing it outside the second floor, it will teleport to the maintainence hatch.)

From the first floor, bring the crate blocking the gate onto the moving lift, and bring it to the left locker. Put it on a pressure plate and stand on the other one. Collect the chemical and the key.

Throw both chemicals into the maintainence hatch. Next, head to the boiler room, and turn on pipe #1, but turn off one of the other two. Head to the top, and head across the lava pit to exit the level.