Engage in a heavy battle to clear the first rooms and hallways of this level. Watch out for the mutants behind the columns. Again you will be attacked from every side, so be constantly on the move. There are several health packages to pick up. Try also to get at the 1-up in the eastern section. Then head on to the room in the south beyond the green barrels. You see the Silver Key behind a barrel, the block next to it is a pushwall. Then venture into the central area. Fight off every enemy and get the Gold Key in the room behind the first set of columns. Now go for the elevator. The first one is a dummy, it includes treasure and two mutants. The next elevator door has an SS behind it. Deal with him and start the long walk up to the elevator control in the north-eastern corner. Don't let the last SS behind the corner surprise you.