The Secret Aquarium

The Secret Aquarium is one of 3 secret courses to appear in Super Mario 64, where Mario collects eight Red Coins to retrieve a Power Star floating amidst a large flooded room. It is a cube-shaped room which the four big, glass windows encompassing all sides of the house are each stained a different color. It is accessed via one of two hidden alcoves in the wall adjacent to the Jolly Roger Bay painting. Though laden with oxygen-replenishing Yellow Coins, there is no surface to the aquarium. The player must, upon entering the level, navigate its depths and collect all scattered Red Coins before Mario's health runs out, for which a Power Star is awarded. Despite its underwater environment, The Secret Aquarium is actually suspended midair in the sky, high above the clouds, bearing a resemblance to the Big House in the Sky from the Rainbow Ride course.

No significant changes were made to this course when it later returned for the Super Mario 64 DS remake, Super Mario 64 DS.