
At the other end is a chaingun approaching it will cause the door to close. Of the three trailers closest to the northeast of the first area, the middle one can be opened from the east.Backtrack to the wall that locked you in the red caves, to the right of it there are red sunken bricks, open them and push the switch behind them, then keep backtracking to the spawn, open red door, shoot the barrels to the left, go through the "crack" they've made, shoot "off" the furthest dirt tile, go left, open door, then the door to the right, lower one of the UAC logos and push the screens on the front.

Backtrack to the silver building, go to the highest floor, open blue door and the yellow door behind it, go right, push switch, go through the door near it that it opened, kill the baron of Hell, push the switch behind the counter, go through the screens it lowered, go beneath the red torches, then beneath the candles, approach the top, go through the opening, approach the idle cyberdemon, kill the two barons of Hell, kill the cyberdemon, take the red key. Get back outside, open the doors on the corner of the silver building, go down the halls, go to the left side of the 3D UAC letters, take yellow key behind the furthest pillar on the right side. Make a 180 degree turn, lower wall, go inside the building in front of you, open its door, open the sign behind it, take blue key.

Sector, thing, and linedef numbers in boldface are secrets which count toward the end-of-level tally.

Letters in italics refer to marked spots on the map.
