Three guards will be here and two imps or chaingunners in the dark area. Explore the rooms they were in to get various items, including berserk. Here, you need to open another switch to proceed, however the traps containing enemies will open. In the next area, turn left and walk the stairs up to a wall which will open. Right there, press the switch to lower the wall. Go forward and take a shotgun in the dark room. Sector numbers in boldface are secrets which count toward the end-of-level tally.
Letters in italics refer to marked spots on the map.