BS L21

BS_L21 is a single-level PWAD for Doom that was released in 1994. It was designed by Brian and Craig Sparks.

Secrets

 * 1) The path south of the pillar with the switch that opens up the route to the blue key has a lift leading to a room with some items. En route to this room is a secret door to the west (marked with a different texture), leading to an outdoor area with two boxes of bullets, 4 shotgun shells (neither present on easy skill), three armor bonuses, 4-6 shotgun guys, and 0-3 imps. (sector 171)
 * 2) The door immediately before the door opened by the aforementioned switch (leading to the blue key area) counts as a secret and is impossible to miss. (sector 81)
 * 3) East of the red door is a path leading to a lift to a health bonus. There is a secret door to the east here leading to an armor. (sector 37)
 * 4) North of the blue door is an alcove with a box of shotgun shells (hard skill only). The back wall of this is a secret door leading to a chainsaw (hard skill only) and a switch which opens up the windows to the outdoor area. (sector 147)
 * 5) The nukage surrounding the yellow key counts as a secret and is impossible to miss. (sector 16)
 * 6) En route to the yellow key area is a path leading to a lift - at the top is a secret area mirroring #3, leading to a medikit. (sector 41)

Current records
The records for the map at the Doom Speed Demo Archive are:

Player spawns
This level contains four spawn points:
 * 1) facing north. (thing 4)
 * 2) facing north. (thing 9)
 * 3) facing east. (thing 10)
 * 4) facing north. (thing 14)

Things
This level contains the following numbers of things per skill level: