|Stories||Kingdom Hearts: Arcana|
|Theme Music||Magical Mystery|
|Battle Music||Working Together|
The Mysterious Tower (不思議な塔, Fushigina Tou) is the first World Nathaniel visits in Kingdom Hearts: Arcana and the third World introduced. It is the home of Master Yen Sid, and serves as a starting point for Nathaniel and Flintlass's journey.
Mysterious Tower is situated in a Countryside, which consists of several hills apparently floating amongst the clouds in the endless sunset, with several stars gleaming in the background. Other than the hills and the tower itself, the only physical existence in the Countryside is a glowing railway along which the single train rides. The Tower itself is a surrealistic, crooked, golden-brown tower, loosely based on the setting of Fantasia's The Sorcerer's Apprentice. Though it appears to be missing several key structures from the movie, such as the well and the basement study, it appears that the segment is canon to the Kingdom Hearts storyline, and this tower is where it takes place. The Tower is topped with blue cone-shaped turret roofs, decorated with moons and stars, similar to Yen Sid's hat. It rests on a floating island that contains a courtyard and many trees that obscure the rest of the Countryside from view.
Inside the main door is a simple round room, surrounded by an upward-spiraling staircase that leads to a strange portal. Through the portal, a person is transported to higher areas of the Tower, where the staircases float randomly. They lead into other portals or doors to other parts of the Tower. Other than the entrance, stairs, and upper floor, there are two known rooms in the Tower, the Moon Chamber, and the Star Chamber. Both are perfectly round rooms, each with two doors leading either up or down the Tower, and are decorated with moons and stars, respectively. The final stairway is steep and straight, and leads to Yen Sid's Study. Yen Sid's study is the largest room in the building, with several shelves containing many books, several about the exploits of King Mickey. There is a large wooden desk behind which Yen Sid sits, and behind it, large star and moon windows displaying the Countryside. A door on the side of the study gives way to an Antechamber, which holds chairs and a large wardrobe.