Near the very end of World 1-2, there is a glitch that allows you to phase through a seemingly solid wall and enter a world that the game appears to have created itself, and given its labelling as "-1", it has been termed by fans as "The Minus World". Prior to this, it was not exactly common knowledge that this was possible; gamers became fascinated with the notion that the game itself has this seemingly redundant code lying about, and with some clever exploitation, players can venture into uncharted territory beyond what even the devs had imagined. It is the sort of flash-in-the-pan piece of accidental awesomeness that doesn't occur often enough, such that this has become one of the most legendary glitches of gaming lore, even if the developers did end up removing it in all later versions of the game. Still, it's a testament to the creative possibilities of games, even when this creation appears to happen by accident.