This level occupies the map slot MAP27. For other maps which occupy this slot, see Category:MAP27.
From the map start go north. Ride up the first lift, go east and descend the stairs. Use the switch in front of you to lower the lift with the blue armor and step on it. After riding it up, push the recessed wall to the east to open a niche (sector 20), containing a backpack, a box of shotgun shells, a box of rockets and a bulk cell.
Return to the map's first lift and ascend the stairs west of it. Upstairs, lower the northern metal wall with yellow lights at the bottom to find an alcove (sector 111) with a soul sphere in it.
Once more return to the map's first lift, go north and take the eastern path at the fork. Enter the room in the east of the bend. The part of the floor where the two stimpacks are on is in fact a lift. Step on it to lower it and straferun, (thus using wallrunning) to the east as there a teleporter far away has lowered and is about to rise again very soon. As you enter it, you are teleported on the pillar (sector 137) with the BFG9000, two (one on hard skill levels) bulk cells and a medikit on it.
As you enter the room where the BFG-9000 is in from the southwest or southeast, you trigger the lift in the north of the room to lower, releasing an arch-vile. Do not kill him instantly, instead run in front of one of the four windows surrounding the northern part of the room and let him attack you to perform an arch-vile jump on the window ledge. Drop down to the large outside area. In the west of the westernmost window you find a room with a berserk pack, 17 health bonuses, an invisibility sphere, a computer area map and a teleporter to get back to the map's first lift. If you killed the arch-vile yet, you can make an attack noise at the edge of the (better still closed) blue door to awake the cyberdemon, let him teleport in and kill him. Then open the blue door and wait for (one of) the arch-vile(s) in the exit room to attack you.