The Secret Aquarium

From the Super Mario Wiki

The Secret Aquarium is one of three secret levels in Super Mario 64 and Super Mario 64 DS, where Mario, or the character played, must collect eight Red Coins to get a Power Star in a large, flooded room.

The level itself is fairly easy, as drowning is the only way for Mario to die while in this place. Also, the many Coins in the level will help prevent Mario's health/oxygen from depleting. There is a Red Coin at the bottom of each of the room's four corners, while the other four are floating around the center.

The entrance to the level is in the same room as the entrance to Jolly Roger Bay. If Mario faces away from the painting and looks at the other end of the room, he will find two holes in walls. The hole on Mario's right contains a 1-Up Mushroom, while the left one is the entrance to the level.

Super Mario 64 / Super Mario 64 DS
Protagonists	Bob-omb Buddy • Mario • Luigi • Wario • Yoshi • Dorrie • Headless Snowman • Hoot the Owl • Klepto • Koopa the Quick • MIPS • Penguin • Princess Peach • Toad • Tuxie
Bosses	Big Bob-omb • Big Bully • Big Mr. I • Bowser • Chief Chilly* • Chill Bully • Eyerok • Goomboss* • King Boo* • Whomp King
Items	Power Star • Yellow Coin • Blue Coin • Red Coin • Silver Star* • 1-Up Mushroom • Mushroom • Power Flower* • Wing Cap • Vanish Cap • Metal Cap
Objects & Obstacles	Bill Blaster • ! Block • ! Switch • ? Block • ? Switch • Blue Coin Block • Crystal Tap • Fire Shooter • Green Shell • Cannon • Star Marker • Crazed Crate • Donut Lift • Lava • Pushy Wall • Pyro Box • Spinning Heart • Star Door • Treasure Chest
Locations	Battle Fort* • Big Boo Battle* • Big Boo's Haunt • Bob-omb Battlefield • Bowser in the Dark World • Bowser in the Fire Sea • Bowser in the Sky • Cavern of the Metal Cap • Chief Chilly Challenge* • Cool, Cool Mountain • Dire, Dire Docks • Goomboss Battle* • Hazy Maze Cave • Jolly Roger Bay • Lethal Lava Land • Rainbow Ride • Rec Room* • Roof • Shifting Sand Land • Snowman's Land • Sunshine Isles* • Tall, Tall Mountain • The Princess's Secret Slide • The Secret Aquarium • Tick Tock Clock • Tiny-Huge Island • Tower of the Wing Cap • Vanish Cap Under the Moat • Wet-Dry World • Whomp's Fortress • Wing Mario Over the Rainbow
Enemies	Amp • Bob-omb • Big Boo • Bully • Boo • Bookend • Bub • Bubba • Bullet Bill • Chain Chomp • Cheep-Cheep • Chuckya • Fly Guy • Fwoosh • Goomba • Grand Goomba • Grindel • Heave Ho • Koopa Troopa • Lakitu • Mad Piano • Manta • Micro-Goomba • Moneybag • Monty Mole • Mr. Blizzard • Mr. I • Piranha Plant • Pokey • Scuttle Bug • Skeeter • Snufit • Spindel • Spindrift • Spiny • Sushi • Swooper • Thwomp • Tox Box • Tweester • Ukiki • Unagi • Unagi the Eel • Whomp • Wiggler
* Exclusive to the DS version.