|Coins||6 ( ×6)|
|Enemy Coins||9 ( ×9)|
Although the castle does not have any stars of its own and therefore cannot save a coin score, it still has collectable coins. The maximum coin count that can be achieved in the castle in 999, by either exiting a level after getting 999 coins, or repeatedly collecting Castle coins and going out of the area and back in to respawn them. This list enumerates the unique coins that can be collected in the castle.
|(Outside the Castle) 2 yellow coins hidden underneath the bridge over moat||2|
|(Inside the Castle) In the main entrance room, 2 pairs of coins beside the staircase||4|
|(Castle Courtyard) 9 Boo Buddies (with yellow coins)||9|
The castle grounds are the starting location when creating a new file, loading a previous file, or dying anywhere within the castle. It features a sunny environment with birds and water sound effects in the background. There is also a cannon next to the lake that unlocks at 120 stars, which is meant to allow you to get onto the castle roof. However, it can be bypassed with precise movement. There is one secret stage on the castle grounds, Vanish Cap Under the Moat.
The first floor is the introductory area of the castle. It contains 4 main courses (Bob-omb Battlefield, Whomp's Fortress, Cool, Cool Mountain, and Jolly Roger Bay), and three secret courses (The Princess's Secret Slide, The Secret Aquarium, and Tower of the Wing Cap). The star door on this floor requires 8 stars to open and leads to Bowser in the Dark World, the first Bowser stage. The door can be skipped with an LBLJ, by HSWKing, or with speed conserved from Bob-omb Battlefield. Additionally, there is a key door to the second floor, as well as one leading to the basement (the intended next area) and a regular warp door leading into the courtyard.
The basement has 4 main courses (Shifting Sand Land, Lethal Lava Land, Hazy Maze Cave, and Dire, Dire Docks). It also contains the pillars normally required to unlock Vanish Cap Under the Moat, although they can be bypassed with moat door skip. The star door in this area requires 30 stars which can be skipped with an SBLJ, and leads to the second Bowser stage, Bowser in the Fire Sea, and Dire, Dire Docks.
Just like the others, the second floor has 4 main courses (Tall, Tall Mountain, Wet Dry World, Snowman's Land and Tiny-Huge Island), along with a star door that requires 50 stars to enter, which leads to the third floor. The door can be skipped using BLJs or HSWKing.
The third floor contains 2 main courses, Tick Tock Clock and Rainbow Ride, along with one secret stage, Wing Mario over the Rainbow. Although there are "endless" stairs on this floor that require 70 stars to pass, they can easily be skipped using BLJs. These stairs lead to the final Bowser stage, Bowser in the Sky.
The courtyard is the location of Big Boo's Haunt, whose entrance is hidden inside the Courtyard Big Boo. There are 9 other regular Boos in the Courtyard, spawned by Courtyard Boo Spawners. If the player has less than 12 stars, the regular Boos do not spawn, and the Big Boo spawns but immediately despawns itself.