At first stages of development, two Zelda expansions for the 64DD were intended for use with Ocarina of Time. One, entitled Ura Zelda, would include alternate more difficult dungeons and new enemies, while the other, Zelda Gaiden, would include a different overworld and a new adventure. While Zelda Gaiden would eventually evolve into the standalone game of Legend of Zelda: Majora's Mask, Ura Zelda was not released on the Nintendo 64 as a standalone game.
Ura Zelda is actually a patch for Ocarina of Time. The 64DD version was designed so that the original Ocarina of Time cartridge would be plugged into the main Nintendo 64 console while the Ura Zelda expansion disk would be plugged into the 64DD that sat underneath the console. Upon the insertion of the Ura Zelda expansion disk, the Ocarina of Time title screen would change slightly, adding a Triforce icon and "Ura Zelda" on the bottom of the logo. The size of this patch was supposedly about 32-64 megabytes, and due to the smaller maximum size of Nintendo 64 cartridges, the game could not otherwise be released on a cartridge.
Eventually, due to repeated delays in production and development, Ura Zelda's release as a 64DD add-on was scrapped, even as the game was finishing production. As a result, there is no 64DD version of this game available to the general public. Due to public demand for the completed game however, Ura Zelda was ported to the Nintendo GameCube where it was eventually released as a bonus disk for those who pre-ordered The Wind Waker.