Princess Peach's Castle/Castle Attic

The Castle Attic is an supposedly hidden and anomalous floor of Princess Peach's Castle, located above the Fourth Floor. While most copies of Super Mario 64 depict the castle with only three floors, some extremely personalised and anomalous copies depict it with more. These rare exceptions are either a fourth floor or an extension to the second floor. However, an attic can sometimes appear above the fourth. It is accessed by clipping into a certain wall of one of the hallways on the fourth floor.

Geography
The Castle Attic's set appearance is unknown, as those who encounter it describe it differently to others. This is likely a result of the multiple appearances and shifting changes in the castle's layout as a result of the Internal Plexus theory.

The most common depiction of the Castle Attic is a large and open area with multiple rooms and branching hallways similar to the fourth floor. The floor consists of a differently coloured wall texture and various new paintings but only four courses. Others depict the room as a common, stereotypical attic with wooden walls and being much smaller.

There are no screenshots associated with the floor, nor are there any mockups or recreations.

Areas
There are multiple areas in the Castle Attic, which seem to vary from different reports. In the stereotypical attic rendition, there is only one area due to the floors small size.

The Shrine of the Green Crusader
The Shrine of the Green Crusader is a shrine similar to The Toad Shrine. It appears as a large statue of Luigi standing on the base of the Eternal Star statue. The Luigi statue uses the same texture as Metal Mario. It is featured in all reports and renditions of the Castle Attic.

The Portrait Room
The Portrait Room is a room around the same shape and size as the Mirror Room on the second floor. It consists of multiple paintings which can't be entered among three portraits of Princess Peach, Mario and Luigi.

The Unfinished Room
Branching off from one of the many hallways is an empty room with a single sign and a door. The sign reads:"'Please do not venture further, the area ahead is incomplete and could cause irreversible corruption to the cartridge. -Nintendo'"Upon entering the door ahead, the game crashes.

Levels
There are four levels in the Castle Attic. They are often hidden among inaccessible paintings scattered around the floor.

Spindrift Safari
Spindrift Safari is a clone level of Shifting Sand Land, using the Cool, Cool Mountain theme. Most textures have been changed, such as pink sand and a light blue pyramid. Spindrifts replace most of the enemies in the course and the pyramid's entrance has been blocked. The geography of the course has been altered slightly, such as the quicksand areas being replaced with lakes of freezing water.

Aquatic Atlantis
Aquatic Atlantis is a clone of Wet-Dry World's flooded town. The theme and most textures stay the same, apart from the water having a tint of green and the layout of the town has been extended. Most enemies from Wet-Dry World appear in this course. In the center of the town is a large fortress similar to Whomp Fortress' fortress. According to some reports of those who encountered the course claim the buildings can be entered, however others claim they can not.

Waluigi's Castle of Chaos
Waluigi's Castle of Chaos is a course with a similar layout to the Unused Level 1 course which shares the same music and skybox as Bowser in the Sky. At the top of the castle is a Waluigi boss, in which he challenges Mario to a match of tennis. Goombas and Koopa Troopas commonly appear in the course, as well as Chuckyas and Whomps. This course has been rumoured to be created by the A.I., as Waluigi wasn't created until 2000. Others theorize the course to be a remnant of the cancelled game Wario Land 64, which could explain Waluigi's inclusion in the game.

Diamond Mario in the Oasis
Diamond Mario in the Oasis is a switch course for the Diamond Cap, a clone of the Metal Cap with a metallic texture and blue particles. The course consists of multiple islands scattered around an oasis with an occasional waterfall. Mario has to jump across the islands to reach the Diamond Switch for the course to be completed. The course, unlike other switch courses, this is the only one which is accessed by a painting.

Trivia

 * Most paintings are inaccessible, even those which don't appear on other floors.
 * According to those who have encountered it, the Castle Attic uses a much slower and soothing rendition of the castle theme, which possibly sounds like this unused track.