Atari gamer Marc Gallo has found a secret hidden Null Room in the game Superman (Atari, 1979). Accessed via direct manipulation of memory addresses in emulation, the room does not appear to be accessible through normal gameplay.
I believe this “room” is really just a memory location intended to store objects when they are off-screen, which can be displayed as a “room” in the game, but isn’t meant to be.
It’s interesting to me since I spent considerable time playing this game, and wrote an article some time ago, about the central role that the map and movement plays in the design of the game.