Open this wall to access the areas behind the shutter windows. At the far end of the first 'L'-shaped hallway is a wall with blue triangles on it (I).Go through the now-accessible yellow door to the exit switch. Go through the teleporter to your left to be teleported back onto the raised walkway. When you reach the other side, flip the switch on the wall to raise the exit walkway (H). Drop down to the left side of the walkway you are on and follow the tunnel to a teleporter (G), and go through. Be prepared, as you will be ambushed by several Chaingunners when you pick it up. Pass through the two red doors (E) and walk along the walkway to get the yellow keycard (F). Go through secret #3 for a shortcut back to the red door near the beginning of the level. Ride it back up to get the red keycard (D). In the next room, stand on the small box in the corner near the door to cause a crate in the middle of the room to lower. Make your way to the end of the hall and through the next door. On the other side of the blue door, flip the light switch next to the door if you like. Head back to the blue door by continuing to follow the path or by going through secret #2. On your way back, you will be ambushed by a group of Imps from a newly opened closet (C).

After you've retrieved it, head back the way you came. To the left is a locked blue door, so continue right along the path until you reach the blue keycard. Return to the hallway and head to the other end (B) and through the door. This lowers the blue keycard later in the level (A). In the next hall, go straight up the short staircase and flip the switch in the room at the top. Go through the door in front of you at the start of the level.

Doom 4 maps for doom 2