MAP21

A level called MAP21 appears in each of several different games and megawads:


 * MAP21: Nirvana in Doom II
 * MAP21: Administration Center in TNT: Evilution
 * MAP21: Slayer in The Plutonia Experiment
 * MAP21: Pitfalls in Doom 64
 * MAP21: Factory: Manufacturing in Strife
 * MAP21: One Flew Over The Caco's Nest in Alien Vendetta
 * MAP21: Undead Nation in Community Chest 2
 * MAP21: Siege in Hell Revealed