It is this Koopa Kingdom-styled region that sits above every preceding world, but below Bowser's grand utopia called World Bowser, with ? Blocks and Coins are scattered throughout the map. It contains seven standard courses, three Enemy Blockades, a Toad House, a Captain Toad course, a Castle, and a Sprixie House.
After completing the castle's courses, Bowser will kidnap the Sprixie Princesses and will create a sparkling Clear Pipe to World Bowser.
- It is called "Castle World" on Miiverse.
- It is the name of the fictional medieval-themed amusement park called "Castle World", rival of another Middles Ages-styled theme park Medieval World in the 2001 comedy movie Black Knight.
- It was the name of the level dubbed "Castle World" that was planned to be the final location in the videogame Banjo-Tooie, but was ultimately cut during development due to time constraints.