Hit this one to lower the bars behind you. Backtrack to the blue switch you passed along the way and hit it to reveal another blue switch. From the top of the ledge, jump to the hall that has the blue key. Head up the stairs on the western part of the map, looking out for an ambush of chaingunners. The first building you come across requires the yellow key, so go past that to the north, around the rocks past the blue switch. Press the lion switch near those bars to open them, and head through into the second part of the map. South of where the key was located, there are red bars blocking the next passage. Pressing it raises a bridge to the key, so get the key now. Run to the lift behind you, take it up, and enter the Hell knight's pen to another switch. Get up there, but watch out for shotgun guys as you flip the next switch. Flip the switch in here to lower a wall revealing a set of steps. Now exit this building (press the lion head to leave the area that had the barons) and head for the building northeast of the key. The switch on the gray wall in front will raise the staircase to the key. Grab the chainsaw and the ground will lower, surrounding you with demons and spectres. Flip it to lower the wall behind you, but watch out for the barons of Hell. Head towards the east end of the building and you will notice a switch here. Enter the building here, and exercise caution when you pick up the super shotgun, because you will be attacked by revenants when you pick it up. Go east, and head for the path that branches east (this path is open because of the switch you pressed where the spectre was. To get the red key, you need to raise some steps and a bridge to it. Now leave this building via the west door and head outside. Get out of the room and press the switch near the door to trigger a lift to your right. Hitting this switch lowers the red key platform visible from the window. When it rises up, open the door on the left side to find a Hell knight and a switch. Press it, head back into the building and to the lift to the north which has just lowered.

From the start, kill the enemies here and open the wooden wall at your starting point to find a switch.

Sector, thing, and linedef numbers in boldface are secrets which count toward the end-of-level tally. Letters in italics refer to marked spots on the map.

Inmost dens