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.