Doom/E2M9: Fortress of Mystery
This secret location in Doom is a small arena. At the start, you are in an room with eight-sub rooms and four barons of hell trying to attack. If you enter the door to the east, you will encounter a large room with cacodemons.
In the first room, the Plasma gun is directly north and is visible, the rocket launcher is to the north east, the chaingun to the northwest, the chainsaw directly south, and the shotgun is to the southeast. For a backpack, head directly to the west. A blue armor should be picked up almost immediately. Barons of hell will close from each of the diagonals.
Once you want or need to leave the first room, head to the eastern door. Open it, and you enter a second arena with 16 cacodemons. A supercharge is in the nukage pit in the middle, and there is more ammo within the second room.
The exit room is at the end of the eastern pillar. However, you will need to open three doors each containing a key before opening the final exit teleporter.
The only secret on this map is the exit area, and is unavoidable.
All the weapons in the map are located within the first room. As such, players in the second room may consider bolting for the exit before they get killed. If they do, they can easily collect any weapons in the first room in an attempt for a revenge kill.