Ura Zelda (partially lost build of unfinished Nintendo 64DD game; 2000)
Ura Zelda (裏ゼルダ in Japanese, translated as "Other Zelda") was an add-on to the Nintendo 64 game The Legend of Zelda: Ocarina of Time for the short-lived Nintendo 64 Disk Drive. The project was shelved due to the cancellation of the Nintendo 64DD worldwide and the discontinuation of it in Japan, and eventually became Master Quest, first released for the GameCube in 2002.
When Zelda 64 switched formats from a 64DD disk to a standard cartridge release, some aspects had to be scrapped or altered to fit the limitations of the cartridge. Director Shigeru Miyamoto planned an expansion for the game, tentatively titled Ura Zelda or Zelda DD, which would offer new dungeon layouts when revisiting the game. It was planned to be released in Japan in 1998, but due to the repeated delays of the 64DD, this did not come to pass. In 2000, Miyamoto commented that Ura Zelda had been completed for some time. Due to the 64DD's commercial failure, Nintendo cancelled the release of Ura Zelda, thinking of different ways to bring it to a wide audience. Ura Zelda, now titled Ocarina of Time Ura in Japan and Master Quest overseas, would finally be released as part of a promotion for The Legend of Zelda: The Wind Waker, where customers who pre-ordered the game would receive a bonus disc containing emulated versions of Ocarina of Time and Master Quest; it was released in Europe in a limited edition two-disc set. However, Master Quest only contained remixed dungeons from Ocarina of Time, and none of the additional items, quests, or dungeons which were rumored by fans.
Ocarina of Time still contains leftovers from Ura Zelda in its code. This includes a "Disk" icon for both the logo and file select screen. Within the game's code, it is revealed DD connectivity, in reality, was very limited - only replacing dungeons, dungeon maps, dungeon treasure chest icons, text and staff credits. Compared to most 64DD games, Ocarina of Time only exchanges these specific files, rather than primarily running off the disk hardware. This goes contrary to what people once believed Ura Zelda was going to be, and lines up with the final Master Quest release.
Datamining from ZethN64 and his team also revealed "The Legend of Zelda: X" to be a possible early name for Master Quest. Since this was found within the Debug ROM, it is theorized this could've been a temporary localization title. 
Since Ura Zelda was speculated to revisit maybe some of the scrapped ideas of Ocarina of Time, fans have speculated over which beta content could've been added, as well as any other improvements that may have been incorporated. These include the removed sword beam attack and the ability to obtain the physical Triforce as seen in the Shoshinkai 1996 trailer. Fans have also theorized the addition of a Wind Temple and an Ice Temple, as certain sections from Ocarina of Time have led some to believe such dungeons were cut from the final game. The fabled "Unicorn Fountain", an area resembling the Great Fairy Fountain which contains a statue of a unicorn head, appears in beta footage of Ocarina of Time, but is absent from the final game; it is also believed to been made accessible. New cutscenes and graphics were speculated to be added as well, in addition to a restored persistent world feature, where objects would remain in a certain state for the duration of Link's adventure, such as broken signs not fixing themselves. These were all concepts marketed in the early DD days of Zelda 64, which fans believed could be incorporated into what they believed Ura to be.
In 2010, a group of fans led by artist ZethN64 attempted to recreate Ura Zelda in a mod called Ura Project, a highly ambitious game which would have added a myriad of new features such as a new protagonist, overworld, plot, soundtrack, and dungeons. The team's inexperience led to the project's cancellation in 2013, and early maps of it were eventually leaked. On August 9th, 2016, another fan known as Alex S on GBATemp.net attempted to finish Ura Project in a new mod, Another Restoration of Ura Zelda, also known as Project ARUZ 2016. Due to a lack of updates, this project is also believed to be cancelled.
July 2020 Gigaleak
On July 26th, 2020 partial source code for The Legend of Zelda: Ocarina of Time was leaked on 4chan, as part of the Nintendo Gigaleak. Included in the files was a folder labelled "ocarina2," a secondary repo copy of the game in which DD data was found in.
Initial digging by psi-hate revealed mini-versions of the dungeons found in the base game. These were maps created to test DD connectivity before the full, redesigned dungeon were created.
Of most significance in the ocarina2 files were early versions of the Swamp Spider House and Beneath the Well from The Legend of Zelda: Majora's Mask. According to the file names, setup, and music cues these were intended to replace The Great Deku Tree and Jabu Jabu's Belly respectively. It is however unknown if these were truly meant to be implemented in an early version of Ura. In a 2015 "Iwata Asks," Ocarina of Time Dungeon Designer, Eiji Anouma admitted he began developing new dungeons in secrecy during early production on Ura:
"I secretly started making new dungeons that weren’t in Ocarina of Time, and that was much more fun to me."
It is entirely possible these two maps were the new dungeons he was referring to, as the maps are far more incomplete and barren when compared to either their final counterpart in Majora or other DD maps in the data.
Other files relating to Ura were found in the folders for standard Ocarina of Time, including an animation of Child Link diving into a chest and a purple version of the logo. Most notably, in the folder labelled \data\shape2\zelda_scene, all the DD map files for the dungeons were found. There are more than several differences when compared to the final release of Master Quest, in terms of puzzle difficulty and actor placement. It is assumed that the changes made for the final release on GameCube were to adjust the game balance to be easier and more accessible.
On November 24th, 2021, ZethN64 released a patch which ported all the original DD maps into the base game. Through the help of Yakumono (LuigiBlood), another patch was subsequently released which restored all intended Disk Drive functionality.
July 2020 Gigaleak Images
- Nintendo 64 Disk Drive (partially found unreleased video games for Nintendo 64 add-on; late 1990s-early 2000s)
- BS The Legend of Zelda (partially lost Satellaview remake of "The Legend of Zelda"; 1995)
- Zelda 64 (partially found beta version of "The Legend of Zelda: Ocarina of Time" Nintendo 64 action-adventure game; 1995-1998)
- Zelda Gaiden (lost beta version of "The Legend of Zelda: Majora's Mask" Nintendo 64 action-adventure game; late 1990s)
- Unseen64 article on the development of Ocarina of Time, which contains information on Ura Zelda.
- An article about Ura Zelda on Zeldapedia.
- A playlist with footage from one of the projects to restore the game.
- The soundtrack from one of the projects.
- Various 64DD maps found in the Gigaleak.
- 64DD map set ups found in the Gigaleak.
- Archived IGN interview with Miyamoto about Ura Zelda. Retrieved 29 Apr '20
- Nintendo Power Shigeru Miyamoto Interview - November 11th, 1998 - Zelda Dungeon Retrieved 19 Feb '21
- Sensei Speaks: Shigeru Miyamoto Interview - IGN Retrieved 19 Feb '21
- Zelda DD Action in '98 - IGN Retrieved 19 Feb '21
- Ura-Zelda Complete - IGN Retrieved 19 Feb '21
- Miyamoto and Aonuma on Zelda - IGN Retrieved 19 Feb '21
- Limited Edition Zelda in Europe - IGN Retrieved 19 Feb '21
- Ura Zelda Leftovers - The Cutting Room Floor Retrieved 19 Feb '21
- Unseen64 article about Ura Project. Retrieved 20 Feb '21
- Reviving Ocarina of Time's long-lost Ura expansion - Eurogamer Retrieved 20 Feb '21
- Archived thread on GCN announcing the cancellation. Retrieved 20 Feb '21
- YouTube video exploring the leaked Ura Project. Retrieved 20 Feb '21
- GBATemp thread focused on Project ARUZ. Retrieved 20 Feb '21