The stairways lead up to bars (2 and 3) that need the blue skull key to open. There are a couple imps and a cacodemon each direction. Hoardes of bull-demons will arrive in the lower area once you have fully explored everything you can get to. There are lots of rockets and ammo all over the place. Once all the bull-demons and barons have been destroyed, the blue key will appear at 1.

To get the rocket launcher and shotgun on the pedastles, activate the switches at the top of the pedastles behind you that lower when you approach the weapons. The backpack and chaingun are reached by running toward them when the platforms are raised.

Collecting the key will get the attention of a group of lost souls. Deal with them before moving up to activate one of the blue switches after you have the key. To get to the BFG9000 in the alcove, search the panel near 3 to open the bars at 4.

Behind either set of bars waits a mancubus at 5. Behind him are imps and cacodemons. In the middle is a pain elemental.

In the inner building are more lost souls. At 6 is a switch that will appear, and opens the door to the last area. A couple of barons and some imps will come at you then. Let the barons waste the imps as they get in the line of fire, then finish them off and move into the room they came from.

There is a soul-sphere in the middle of the next room, but picking it up will call in some cacodemons to attack you. Back up down the hall and rocket them into oblivion to keep it. There are several zombies that need to be dealt with also.

A nightmare-demon haunts the corridors down the stairs N and S. These paths lead to lifts up to the exit area. A few more zombies and a cluster of lost souls around the exit, and that is it for this relatively small level.