This level occupies the map slot MAP13. For other maps which occupy this slot, see Category:MAP13.
From the map start follow the upper walkway. At the east of the map, after the room with the rocket launcher and right before you open the first door, turn east. Shoot the gargoyle face to raise the blood pit's ground so you can grab the box of bullets, the box of shotgun shells and the box of rockets (sector 165). From the raised "bridge", jump over to the mancubus stage in the south to find a chainsaw.
Enter the door mentioned in secret#1 and ascend the stairs. As you approach the red skull key, downstairs a passage (sector 125), marked by an arrow on your map, opens. Use the teleporter at it's end to get to a higher type 7 damaging floor with a soul sphere.
Follow the walkway behind the red door. As you approach the stairs with a bullet box and a shell box on it, a room with a revenant and two rockets in it opens in front of you. In here, the western part of the northern wall has a misaligned texture. Open it and use the teleporter. You will land up in a secret room (sector 173), containing a plasma gun, six clips, three sets of shells, six rockets, four energy cells, two backpacks, two medikits and a blue armor.