This is a recording of DOOM v1.2, episode 3, level 9 (secret, called WARRENS), 
played at the Ultra-Violence mode with no cheat codes, and using only the 
weapons available on the level.  Don't be fooled by the fact that it starts
out as if it were the first level of the game, it gets harder very quickly.

In case you were wondering how to reach the secret level...you get there from
level 6, called MT. EREBUS.  (The level with all the buildings placed in a red
sea of fire)  There is a pylon with a walkway around the top, located in a blue 
sea.  You get to the pylon via a hidden teleporter in a green building with 
four brown imps in cages outside the front door.  If you walk all the way 
clockwise around the walkway, you can see an open blue room below, with a skull 
switch.  You CANNOT jump into the room, but you CAN turn your back to it, and 
use the rocket launcher to fire into the wall.  This will propel you far enough 
to land inside the blue room.  It goes without saying that you had better have 
close to 200% life and armor before attempting this stunt.