The Bowser Room

The Bowser Room is a single, hidden room in Super Mario 64. It is a small room with a white floor and grey walls, and a picture of Bowser hung up on the wall. The purpose of this room or how to access it varies from copy to copy.

Versions
There are a few different versions of The Bowser Room that players have stumbled upon. There are currently only 2 videos that have concrete evidence of the room's existence. Both videos do depict the room in seemingly different states of development.

This video, by user Captain Swag, enters The Bowser Room by BLJ-ing into a hidden warp above the waterfall outside Peach's Castle. The room almost looks exactly like the screenshot of the room, but there is furniture and a door on the other sides of the room. There is no proper end goal and the video abruptly ends with the user's Nintendo 64 crashing.

This video, by user jefftastic, enters The Bowser Room by entering the warp that takes you to Secret Aquarium. The room is textured far differently from the screenshot, and is expanded much more than the one depicted in Captain Swag 's video. The furniture pieces are different and considerably more lower detail. The goal is to collect 8 red coins, in which the user does and is given a star as a reward. The video ends after the user saves the game.

This video by marionova64, enters The Bowser Room through a door located in Bowser's Domain. The room is textured differently from the screenshot. The room seems to resemble a battlefield, where the Koopa King is fought. Interestingly enough, the paintings in the wall resemble images from Greenio's tapes, specifically, from the first ever lost tape. As a final note, the room uses the song made by Planet Bobstar, which could confirm that his songs are not fanmade and are actually real.

Theories
Within Greenio's Lost Tapes, a room very similar to the Bowser Room appears in the video for 05.30.97. This implies that the Bowser Room is associated with the scrapped "bad" ending for Super Mario 64.

The two videos showing concrete evidence of The Bowser Room could be showing two versions of it during different times in development.

Trivia

 * It is said to be Miyamoto's favorite room. Unconfirmed development transcripts have recorded that he insisted that the room needed to be programmed in the game before it was finished.
 * The Bowser Room was mentioned in an Oney Plays Crash Bandicoot stream.