Level by hannon13
Walkthrough by DJ Full
In the pool, you don't need to pull the switch but only to get close to it for the door to open. Swim through, get close to another switch or pull it and exit through the second door. Resurface, get out of the water, grab a medikit from the far end of the room, find a switch close to the S bank of the pool, get close to it or pull and go through another underwater door. Follow the passage, resurface when possible, get out of the water, go downstairs and fall into another pool. Swim through the huge passage, find a hole above you and resurface. Get on the dry ground. You can shatter the electronic box on your left, but don't fall neither into the pit on the right of it, nor into another one in the NW corner - there's no way out of them. Collect the compass from the pedestal. You can't open the cabinet and do anything else here, so it's game over.
EDIT: I was wrong - the trigger for the cabinet is set on the square containing the shatter box. You can stand on it and watch the cabinet open and close. That's terrifying I didn't hit on this idea by myself. Obviously, I've partially lost the habit of thinking due to the fact I play too much trash levels recently. Sorry, fellas!