DOOM sixth secret room
On the plateau near the giant’s head there is a cave, you need to enter it.
Among the rocks and ledges, hidden lever to the left of the skeleton in a helmet The Elder Scrolls 5: Skyrim.
Emerging from the cave, head to the right side.
Go down the ruined stairs and turn left.
The rock immediately visible pass. Be careful, there is a cavity, textures hidden inside the room.