The Legend of Zelda: Ocarina of Time had portals, before Portal.
He had previously revealed their existence in an interview with MinnMax, but yesterday also shared actual footage in a tweet.
While it looks a little like the Forest Temple, Goddard clarified he simply asked an artist for some test data to use.
In the MinnMax interview, Goddard (who was also responsible for the Spaceworld 1995 Zelda tech demo) worked on a separate tech demo to push the capabilities of the N64 console.
"Recently I found an old directory of source code that I had backed up, and it was the first map of the N64 Zelda, just with Hyrule Castle," he said. "So I was doing all these experiments.
"You had a portal where you could look through, go in and you'd be teleported to a different part of the map. You'd see through the door to a different part of the map, walk through it, then walk back through it, if you see what I mean.
"It was very cool tech and I had it running and showed it to some guys at the office here and they said 'oh, you've got to put this on the internet', and I said 'well, I can't, really, it's not my property, it's Nintendo's."
He continued: "It was R&D for the game, basically. It was, what could we do with the hardware on the N64? It was basically a demo of actual portals that you could see through to other parts of the map."
Portal was released a decade later, but Goddard got there first. "When I saw Portal I thought 'oh, actually, I had that running on the N64, I should have released it then'," he joked.