One of the original tech demos for The Legend of Zelda: Ocarina of Time had functioning portals, which was a gimmick that would later be popularized by Portal. Ocarina of Time is one of the most highly-acclaimed video games of all time, but many secrets of its development were only revealed within the past year, as part of the Nintendo Gigaleak.
The early screenshots of Ocarina of Time showed areas of the game that never made it into the final product. Fans puzzled over the screenshots for years, with many wondering how different the game could have been. Beta content from Ocarina of Time was revealed in the Nintendo Gigaleak, while a prototype version of the game was later found on an F-Zero X development cartridge. It's clear that many of the early screenshots came from a time when Nintendo was still working out the limitations of the new 3D hardware of the N64. As such, a lot of areas were reduced in scope, in order to ensure the game was able to function properly.
New information about the testing phases of Ocarina of Time has been revealed in an interview on the MinnMaxShow YouTube channel. Giles Goddard was interviewed about his time at Nintendo. Goddard worked for Argonaut Games in the '90s and helped develop early 3D titles, like Star Fox and Stunt Race FX. He also worked on the demo of Ocarina of Time that was shown at the Shoshinkai trade show in '95. Goddard revealed that the content in the demo was more of a proof of concept, but he was able to create something impressive that never made it into the final game.
Goddard revealed he still owns some of the early source code for these tech demos of Ocarina of Time, and it included a map of Hyrule Castle. These maps had functioning magical portals that the player could use to travel to different places on the same map. They could even see what was going on on the other side. The portals were connected to crystals that could be flipped, showing different parts of the map. When asked why it wasn't included, Goddard said that it was too far into development to include such a major new element, so the portals never appeared in Ocarina of Time.
The ability to instantly create functioning portals and use them in interesting ways would later appear in Portal, which is another beloved title that was released nine years later. It's interesting to think how Ocarina of Time (or one of the later Legend of Zelda titles) could have used this concept in its dungeons, as it could have predated Portal by nearly a decade.
Source: MinnMaxShow/YouTube