There is a door which appears to go nowhere. The room has the large container pouring hot liquid metal in the middle, on the first floor in the corner is a sliding door, and some liquid metal in a pit. Use the cooled metal to jump across the pit and reach ammo and pain killers on the other side.
Enable "Cheat mode". When you kill the men that are in the room in front and to your left, go through the door where you have to turn the valve. After that, go across the walkway into the room with all the laser beams. Blow them up and continue out the other door to the other side. You do not have to destroy these lasers -- simply watch out for the flames. Go around the corner and kill the man, then face the door that the man was in front of and enable the noclip code. Walk through the door and get the hidden ammo.
There is a laser grid at the very startof this area. To get past this, simply shoot what the laser comes out of, but stand back because the explosion is big.