This level occupies the map slot MAP02. For other maps which occupy this slot, see Category:MAP02.
From the map start, climb the stairs, push the switch to your left to open the lower door and enter it. In the next room, go straight through the easternmost door. Now you are on the top of some long stairs: on the third stair from above, push the wall below the lantern to reveal a switch. Use it to lower the pillar (sector 78) with the soul sphere on it in the northwest of this room.
As you reach the last step of the stairs leading to the red key, you trigger a corridor with a hell knight and a teleporter in it to open temporarily in front of you. Do not enter this corridor yet as you cannot open it from inside. Instead kill the hell knight from the top of the stairs, reopening his hideout by crossing the triggerline whenever needed. By now you should have a feeling how long the corridor stays opened each time. Step on the socket where the red key was on and wait until the corridor closes again. Run down the stairs, thus not only opening the corridor behind you, but also lowering another wall: At the bottom of the stairs make a hairpin turn to the left and enter the room just north of the switch you used to lower the pillar from secret #1. If you made it in time, the wall in the southwest of this room still is lowered, revealing a secret room (sector 278) containing a super shotgun and three sets of shotgun shells.
Inside secret #2, open the northeastern wall to exit the room. Enter the door in front of you and simply push the slightly recessed brick wall just in the east of the door to open an alcove (sector 281) with a rocket launcher and two rockets in it.