Deep, Dark, Dungeon

Deep, Dark Dungeon is an unused stage that can manifest in certain copies of Super Mario 64 and is usually found on the First Floor.

Overview
The Deep, Dark Dungeon is a spooky and ominous dungeon filled with dangerous obstacles and enemies. After completing the mission “Blast to The Top of The Dungeon” you can blast through a cannon to go to a subarea called Sunny, Sunny State.

Sunny, Sunny State is a luxurious beachfront area with crystal-clear waters, sandy beaches, and towering palm trees. The level is reminiscent of the Beverly Hills area in Los Angeles, with opulent mansions, luxury cars, and exclusive clubs. According to the mission names, Mario owns a mansion here.

Missions

 * 1) IN THE EMPTY CELL
 * 2) LOCKED BEHIND BARS WITH 8 RED COINS
 * 3) BLAST TO THE TOP OF THE DUNGEON
 * 4) FIND THE SUNNY STATE
 * 5) INSIDE MARIOS MANSION
 * 6) DOWN THE HIGHWAY
 * 7) 100 COIN STAR

Theorizing
It is commonly theorized that this level was used to test the way that the Personalization A.I. handled generating levels, with the main area being a test of how the A.I. would generate dark, bowser-like levels, with Sunny, Sunny State being a test of how the A.I. would generate happy, cheerful levels.