The Legend of Zelda: Ocarina of Time Master Quest

"The Legend of Zelda: Ocarina of Time" came out on the Nintendo 64 to much acclaim. Nintendo then created an alternate version of the game called "The Legend of Zelda: Ocarina of Time Master Quest" that had the same quest but the dungeons and puzzles were changed. This was originally intended to be released on the Nintendo 64dd a disk drive attachment for the Nintendo 64. But due to poor sales of the disk drive, the game was stuck deep into Nintendo's vault instead of being released.

However, when Nintendo went to release The Legend of Zelda: The Windwaker on the Nintendo Gamecube, they decided to release a bonus disk containing both The Legend of Zelda Ocarina of Time and  Master Quest. Finally, fans were able to play the Zelda game they had been missing.

Nintendo also released a special Gamecube bundle that had the Windwaker, Ocarina of Time and Master Quest all in one package along with the system. Needless to say this Gamecube disc is no longer being manufactured and Master Quest has not been released on any other systems. So if you want to play the game (legally) you'll have to try rounding up the disc somehow. You can try  here, here, here or here. Also check your local craigslist, you never know what will show up there. Good Luck!