You start in the same outdoor area in which you found the elevator on the previous floor.
This level offers a lot choices of moving making it develop differently each time you play it.
There are only guards and officers in the first areas. If you are without a machine gun, there is one in the secret area in the northern part of the floor, accessed from the red brick section. A 1-up is found inside the blue maze.
After a lot of varied action you will get to the grey brick section in the south-eastern area. The Silver Key is hidden behind the green barrels.
After clearing the south-western area don't forget the chaingun behind the pushwall if you not already have one. You will need it.
Then you confront Hans Grosse. Get to the ammo and health and start running around the parallel walls while fighting him. Once he is defeated you take the Gold Key and enter the next room. Only to meet another Grosse! Get him out of the room and push the wall by the 1-up for more ammo. Fight him till he is defeated or you run out of ammo. Then make it to the exit.