DOOM level 11 Necropolis secret room
Lever location: First you need to get to the room with thick pillars, at the top of which is pulsating red (pink) energy. In the far wall of the room there are three niches (average closed bars). You need to get to the right niche. The pile of skulls is a lever that you, of course, need to be activated.
Secret room location: Get out of the room with columns. Walking up the stairs, turn left, then turn right and go through the passage. Go forward until the end. When you hit the wall, turn right and you will see the entrance to a secret location.