Blue key[edit]
You will first need to obtain the blue key; it is located in the south-eastern corner of the map.
From the start, head through the corridor on the left. In the circular room, you can optionally head to the right and to collect blue armor.
When you head down the staircase, a door will close behind you for 30 seconds. Meanwhile, you will encounter a large room that is full of demons. If you have trouble with them, you can use a berserk pack in the southern part of the room, or the invulnerability in the south-east corner.
Flip the switch in the south-west corner to reach the courtyard, where you can collect the blue key. If you want some ammo, you can flip the switch to the left to open a nearby door.
Yellow key[edit]
The yellow key is in the middle of the map. From the starting area, the blue key door is located to the right of the entrance. Head through the blue key door, and take the path to the south-east. You will enter a room containing the yellow key, which you can take from here.
From the blue key door, you can also collect a chaingun by taking a right turn, or collecting a backpack and other ammo by going to the southwest.
Red key[edit]
The red key is located in the southern part of the map. To reach it, head south from where you got the yellow key.
Go through the yellow key gate, and head to the end of the corridor. Open the door on the right, clear out the monsters, and enter the alcove. Flip the switch to lower the red key.
The other two rooms in the yellow key area only contain monsters.
Exit[edit]
The exit is located to the west of the blue corridor area. When you open the red key door on the north end of the exit room, flip the first switch; thus reveals the true bridge switch and releases a cacodemon. The second switch raises a bridge to the exit.
Secrets[edit]
- When you approach the coutyard containing the blue key, climb up the stairs to the left to enter a room overlooking this courtyard. This room leads to a side room with a switch; use it to open a supply closet with ammo, invisibility and a computer map. (Sector 250)
- From the start, run past the blue key gate into a corridor with UAC logos. A doorway leads into a darkened area; enter this area to claim the secret. On the left hand side of this darkened area is aa plasma gun. (Sector 284)
- In the darkened area, there is a switch to the right. Use it to open the door and access a chainsaw. {Sector 301)
- In the room west of the exit, one of the side slime pools contains a path to a secret area. There's also a teleporter, and a rocket launcher. (Sector 44)
- If you take the teleporter in the previous secret, you will enter a small room with two demons and a red key door. Open this door to reveal a switch. (Sector 72)
- You need to use two switches to open this secret. The first switch is visible when taking the southern path past the blue key door. The other switch in the above secret, behind the red key door. When they are both used, a soulsphere and cell charge pack are reveled near the entrance. (Sector 294)