DOOM level 12 VEGA Central Processing secret room
Lever location: Passing the twelfth level you need to get the blue card-key that opens the door to the “blue castle”. You will find yourself in the corridors. Enter the first door, which is on the left. Now go to the other door with the “Blue Castle” (it is on the right). Soon you will stumble on a corpse, which lies near the boxes. Behind these boxes is the lever.
Secret room location: Leave the room with the lever and follow to the place where they came from, past two doors with “blue locks.” When will find yourself in the corridors, and you will have a choice of where to go: to the right or to the left, select the last option. Now go ahead and soon you will reach hidden areas.