Quote from the video:
"This is an unused track in Mario Kart 8. It loads when you request the course that has ID 0x00 (not normally selectable, but we forced it to load with a course ID hack). And what an oddball track it is!
The game calls this track "Gu_Menu", but we call it "The Void" for obvious reasons. Clearly a track never designed to be driven, ever. Its official name indicates that it's a placeholder track for the main menu or something similar (which begs the question, why does the main menu need a placeholder track?)
Now that we've had chance to look at the filesystem of the game disc, we've learned a bit more about it. It's missing some files that other tracks have, but the game clearly doesn't mind that and is happy to load it. It has it's own folder on the game disc under the name "Gu_Menu", it has a solidity mapping, a course model/texturing (though it obviously doesn't render), minimap graphic and start line and object positioning. It would seem that's the bare minimum required in order to load a track.
This track appears differently just about every time you see it, mainly due to its bizarre property of not clearing the screen in between render frames; meaning that anything that is on the screen persists unless something comes to overwrite it. This can lead to some really neat looking graphic effects.
As a track, it's just a square of solidity in midair. You can fall off, and you get respawned (the respawn is instant, Lakitu is not involved in it). There are no checkpoints, item rotues, CPU routes, minimap or other similar properties. There is also no music, and its little preview icon is nothing but a white square. It is literally just an invisible square with a trippy rendering method."