Adventure (Atari 2600): Developer Room
This screen from the Atari 2600 game Adventure is heralded as the FIRST ever secret level. For that reason, it deserves a spot on this list. Adventure was published back in 1980 when game developers weren’t supposed to take any credit for the games they produced. Warren Robbinett, the man responsible for Adventure, didn’t like that. He went behind the backs of his superiors and stuck his name deep within a secret level of his game.
Super Mario Bros. : Minus World
Minus World. This is by far one of the most recognizable secret levels in gaming, and may be the most famous secret level of all time. Minus World is a single level that was supposed to be marked 36-1, but is displayed as -1 due to a glitch displaying the number. The level is an exact copy of level 7-2, except that the pipe at the end of the level (shown above) is glitched and sends Mario back to the beginning of the level. This effectively dooms Mario to death by timer countdown or enemy- there is NO way out.