Secret Aquarium

The Secret Aquarium is a hidden level in the entrance room of Jolly Roger Bay by jumping into a hole in the wall. It is a large brick room in the shape of a square with windows on the walls. It is filled with water. There is a star for collecting 8 red coins.

Title Screen Level
There is a supposed Title Screen Level that, after following several steps, will replace the Secret Aquarium.

Aquarium Limbo
There is a supposed version of the Secret Aquarium known as the Aquarium Limbo that has white bricks and a Big Boo's Haunt skybox.