Princess Peach's Castle

Princess Peach's Castle is the main hub world of Super Mario 64. Nearly all courses and levels are accessed in Princess Peach's Castle. There are several floors.

Castle Grounds
The Castle Grounds is an area that surrounds the castle. It is where the player starts. The only level accessed here in unpersonalized copies is Vanish Cap Under the Moat.

First Floor
The First Floor is the first main area of the castle, accessed by the Castle Grounds. It usually contains Bob-omb Battlefield, Whomp's Fortress, Jolly Roger Bay, Cool, Cool Mountain, Princess' Secret Slide, Secret Aquarium, Tower of the Wing Cap and Bowser in the Dark World. It also contains the paths to the Second Floor, Castle Courtyard, and Castle Basement.

Castle Courtyard
The Castle Courtyard is a sub-area of the First Floor. It only regularly contains the path to Big Boo's Haunt, and also has the L is real 2401 statue.

Castle Basement
The Castle Basement is the second main floor unlocked in the game, unlocked after beating Bowser in the Dark World. It usually contains Hazy Maze Cave, Lethal Lava Land, Shifting Sand Land, Dire, Dire Docks, and Bowser in the Fire Sea. Other notable things here are the first toad that gives the player a star, both encounters with MIPS the Rabbit, and the pillars needed to drain the moat and unlock Vanish Cap Under the Moat.

Second Floor
The Second Floor is the third main floor unlocked in the game, unlocked after beating Bowser in the Fire Sea. It usually contains Wet-Dry World, Snowman's Land, Tall, Tall Mountain, and Tiny-Huge Island. This is the only floor that only requires a certain amount of stars to pass, and contains the Mirror Room. In the DS remake of Super Mario 64, it also contains Chief Chilly Challenge.

Third Floor
The Third Floor is the last main floor unlocked in the main game. It contains Tick Tock Clock, Rainbow Ride, Wing Mario Over the Rainbow and Bowser in the Sky. It also contains the endless stairs.

Rec Room
The Rec Room is a sub-area of the First Floor that is exclusive to Super Mario 64 DS. It contains several minigames, Sunshine Isles, and Goomboss Battle. Peach's Balcony is also located here.

There are also several rumored floors and sub-areas of the castle added by the Personalization A.I.

Fourth Floor
The Fourth Floor never has a consistent way of accessing it. It is often claimed to be a large maze, though several reports have claimed it functions as an actual floor. It contains the Internal Garden, a garden area inside the castle, and the Toad Shrine, a large statue of a toad.

Castle Dungeon
A sub-area of the Castle Basement, the Castle Dungeon leads to Fox Forest and Bully Beach.

Bowser's Domain
Bowser's Domain is a hidden area that was first documented by youtuber Marionova64. Bowser's Domain is accessed by jumping past an invisible wall blocking people from accessing the Bowser painting in the hall that leads to Bowser in the Dark World, and falling through a second trapdoor. The area itself is a large maze. There are notable areas such as the starting room, Luigi room, mirror room and Koopa library. In the "Luigi room", there is a painting of Luigi that when entered, will unlock Luigi as a playable character. There is also a variation of the Bowser Room found inside.

Fifth Floor
The Fifth Floor is unlocked after clearing Dire, Dire Docks Village. It contains Burning Meteor, Dark Heaven 2, Robo Station Way, Stanley's Showdown and Reginald's Last Stand. It also has a room that leads to every village in the game except for Eternal Village.

Fifth Floor B
Fifth Floor B is unlocked by collecting the star in Eternal Village. It only consistently contains Robo-Luigi.

Third Basement
The Third Basement functions as a Bowser level, with a boss fight against Dark Matter, the ally of Reginald.

Third Basement B
An extension of the Third Basement with a star after some platforming.

Castle Garden
A replacement of the Castle Courtyard.

Floor 2B
Unlocked after getting a Big Boo's Key, it contains Toxic Cavern, Boiling Hot Basalt, Dry Bones Desert, the Switch Dungeon, and Bowser in the Randomized Realm. Notable rooms in it are the flooded hallway, and the block room, which leads to the Switch Dungeon.

Elevator Room
An elevator that can take you to any floor you've unlocked.

Goomba Courtyard
A replacement of the Castle Courtyard, found by jumping over a fence in the Castle Grounds. It is filled with Goombas.

Hotel Floor
A floor after the Fifth Floor, designed like a hotel.

Internal Plexus
This refers to the general grouping of the areas hidden in the castle, as the castle's layout is not like a castle. There is also the theory that the castle is the veins of the Personalization A.I., with this layout oddity being part of the theory.