I am playing the original doom and I am stuck in the Deimos Lab level. I have found where the exit room is but I can’t reach the exit. Both of the teleporters in this room lead back to the entrance. I have gone back over the entire level and I can’t figure out what else I am meant to do here.
Go back to the room where the exit door is. To the left of the door is a portal. If you look on the wall opposite of this you will see a skull on the wall. Interact with this and it will raise a platform you can use to gain access to the exit portal.