DOOM level 10 Titan’s Realm secret room
Lever location: After opening the door skull head down and go through the two columns with a red (pink) energy. Here is an open passage with a burning torch. Near the pass, turn left and walk to the lattice. Now turn right and activate the lever.
Secret room location: Climb the stairs, the passage which was previously closed bars. Once inside the room with acid, go through the passage to the right, flanked by torches set fire to the green. Go down the stairs, turn right and go straight. Soon you will be taken to a hidden level.