Doom II · PC (MS-DOS) · 1994
Two hidden levels rebuild stages from id Software's earlier Wolfenstein 3D, and the second ends with four corpses of Commander Keen — the hero of id's pre-Doom platformer — strung up on ropes that must be shot to finish the map.
Doom II hides two secret maps that double as a tour of id Software's own history. MAP31, "Wolfenstein," recreates the first level of Wolfenstein 3D using imported Wolfenstein textures and SS soldiers in place of Doom's usual demons; a hidden exit there leads to MAP32, "Grosse," named after Wolfenstein's boss Hans Grösse, who is replaced in the Doom engine by a Cyberdemon. The deepest in-joke waits in Grosse's final room: four hanging corpses of Commander Keen, the kid hero of id's 1990 platform series, dangle from ropes and must all be killed to open the exit. The intermission text before the map reads "You'd better blaze through this one!" — a wink at Keen's real name, Billy Blaze. Together the levels form a deliberate crossover linking three of id's franchises inside a single secret.
On MAP15 ("Industrial Zone"), reach the exit area and take the hidden secret exit to be sent to MAP31. In MAP31 ("Wolfenstein"), find its secret exit to reach MAP32 ("Grosse"). Fight to the final room and shoot all four hanging Commander Keen bodies to open the level exit.