Hollow Horror Halls

Hollow Horror Halls is a supposed secret level in some personalized copies of Super Mario 64. It has 2 main manifestations, a smaller level and a course. It is consistently described as a maze of halls with several Boos, though the exact geometry has never been noted to be consistent between reports. It is possibly a beta version of Big Boo's Haunt, the unused 37HORROR2 level, an early Vanish Cap level (See Version 2), a remnant of the inside portion of Big Boo's Castle, or perhaps a different level entirely. This video appears to demonstrate the music of Hollow Horror Halls, though some reports state the level shares the music with Big Boo's Haunt.

Version 1
This version of Hollow Horror Halls is a course usually found somewhere in the Castle Courtyard, usually either in a hidden room or replacing Big Boo's Haunt. It is a large, dark, and foggy maze of rooms connected by several hallways. The walls are brown brick, with the floor being dark blue carpet.

Missions
"1. CENTER OF THE HALLS""2. HIDE & SEEK FOR RED COINS""3. VANISH BEHIND THE MIRROR""4. DASH TO THE CAGED STAR""5. 5 SECRETS LOST IN THE HALLS""6. THE WAY UP""7. 100 COIN STAR"

Center Of The Halls
In this mission, the player has to reach the center of the course. The room in the center will contain a star.

Hide & Seek For Red Coins
In this mission, the player has to find 8 red coins throughout the course for a star. Oddly, in some reports, all red coins are absent.

Vanish Behind The Mirror
In this mission, the player has to use the Vanish Cap to go behind a mirror somewhere in the level for a star.

Dash To The Caged Star
In this mission, the player has to use the Vanish Cap and reach a cage containing a star after pressing a purple switch which spawns some boxes allowing the player to reach the cage. It appears similar to the "Quick Race Through Downtown" mission of Wet-Dry World.

5 Secrets Lost In The Halls
In this mission, the player has to find 5 secrets throughout the course for a star.

Big Boo's Passing Through
In this mission, the player has to navigate the course until finding a Big Boo. This Big Boo has to be defeated for a star.

Version 2
This version of Hollow Horror Halls is a level usually found somewhere in Princess Peach's Castle by falling through a hole in the floor. It is smaller than version 1, though is still a maze. It is still dark and foggy with dark blue carpet, but the bricks are dark blue as opposed to version 1's brown bricks. Notably, this version tends to have the Vanish Cap switch.

Star 1
This star is collected by finding 8 red coins.

Star 2
This star is collected by finding 5 secrets.

Star 3
This star is found in a hidden room only accessible by passing through a mirror using the Vanish Cap and entering a door leading to the room with the star.