Final Doom Easter Eggs

In TNT: Evilution, Map 17- Processing Area, there is a secret and inaccessable room just to the west of the blue key room. It is used for holding Demons for teleportation into the level, however if you type the noclip code and walk into this area you... more

In different levels of Final Doom, you can find blood splatter on walls that, when you look closely, say "ROMERO". It's very interesting, and they're scattered throughout Final Doom. They're not too challenging to find (I found two, myself, a while ago).