Top left: in Super Mario 64, the room containing the secret entrance to the Princess’s Secret Slide in Peach’s Castle is accessed without a loading screen directly through a door.
Top right: in Super Mario 64 DS, the room has been heavily redesigned and a loading transition has been added after going through the door.
Bottom: Viewing the Super Mario 64 DS files in a model viewer, we can see that the original room is still there in the remake, blocked off by a wall. Since both the wall and the loading zone to the redesigned room block the way, the original room is impossible to access.
In Super Mario 64, rooms in Peach’s Castle load into memory when Mario approaches the door. However, the entrance to Hazy Maze Cave only starts its rippling animation when Mario enters the room it is in. By moving the camera to be able to see inside the room before Mario enters it, it’s possible to see that the entrance is blue before its animation starts.