In terms of video game legends, it's up there with the best of them. A secret world accessible in Super Mario Bros.! A gateway to an underwater stage you can never leave! A hidden, secret zone that only the most elite Mario Bros. enthusiasts will ever find!...
It was the stuff of playground hearsay back in the '80s and '90s, but contrary to many of the other urban legends that popped up around the Super Mario series, SMB's 'Minus World' was, indeed, real and accessible to anyone who cared to study the method to get there and pull it off.
Of course, the reality of this area — the result of a warp pipe glitch that takes you to an inescapable recreation of underwater level 7-2 — is far less exciting than the imagined topsy-turviness the name suggests. Dubbed Minus World because the stage title screen displays '-1', the glitch is tied to how the game reads collision for Mario and subsequently assigns different data to the warp pipes found at the end of World 1-2, sending you to 'World 36-1', which is displayed you the player as 'World -1'.