- Nominating for deletion - This seems better suited as a blog or forum post.
A Hidden interior is an area in the game that is not part of the outside world. Thanks to some glitches, It's possible to get out of a building (i.e. The Main Building) and staying in the interior.
When you get out of a building, you can see a picture in the background. In fact, It's an earlier screenshot of the exterior universe.