A secret level in Super Mario 64
On the ground floor of Princess Peach’s castle, one of the first magic doorways leads to the Jolly Roger Bay. Before you hop into the picture-frame that transports you into the level look at the walls of the gallery room.
Mario can see two tiny black passageways that he can jump and climb into. One only conceals a 1up mushroom, however the other is portal to one of the castle’s secret rooms. If Mario walks through this doorway he finds himself in the centre of a giant cubic aquarium.
Collecting all 8 red coins in this level will reveal one of the castle’s secret power stars.