The Bottle
From the Super Mario Wiki
The Bottle was an item in Super Mario Sunshine that soon became a secret stage. In one of the Noki Bay episodes, the Noki Elder shrinked Mario, in an unknown way, and put him inside the bottle. Inside the bottle, there were many Coins as well as eight Red Coins. If Mario collected all the Red Coins, he would receive a Shine Sprite and finish the episode.
There are many Cheep Cheeps swimming around the bottle, making it hard for Mario to get the red coins. The bottom of the bottle has sand, with a sand castle-like place as well. It has been noted by fans, that there is a mysterious half-opened door on the side of the sand castle, that Mario cannot enter. However rotating the camera would reveal a mysterious book. It is unknown what the book does, and why it was put there, but it serves no purpose in the game.

