Hollow Bastion

Hollow Bastion is a world from Kingdom Hearts and Kingdom Hearts: Chain of Memories.

The Hollow Bastion is a colossal castle that towers above the rest of its world, the Radiant Garden. At one point, it was the only remaining part of the world, along with the waterways beneath it. Hence, the world itself was known as "Hollow Bastion" in Kingdom Hearts and Kingdom Hearts: Chain of Memories. For most of Kingdom Hearts II, it was named this as well. However, it regains its original name by the end of the game.

Unlike the rest of the Radiant Garden, which poses as Final Fantasy's world, the Hollow Bastion has no relation to Final Fantasy whatsoever.

The boss of the Hollow Bastion (on the first visit) is Maleficent, though Riku is also battled. On the second visit, the boss is the Behemoth.

History
Hollow Bastion was a glorious castle owned by Ansem the Wise. Much of the history of the castle is unknown, other than that Ansem ruled the Radiant Garden from it. However, eventually Xehanort took over, and remodeled the castle to include multiple machinery. The result was a twisted bastion; half beautiful castle, half distorted factory. Maleficent, during her reign of the castle, made additional changes as well. It is probable that she either created or remodeled the castle's keep, which has decorations and models of roses and her thorned plants.

Trivia

 * Part of the original music for Hollow Bastion involved a segment from the Sitar Concerto No. 2
 * Kairi was born in the Hollow Bastion, where she lived with her grandma. The current whereabouts of the grandmother are unknown.
 * Hollow Bastion poses almost like a world for two Disney movies. One was Sleeping Beauty, while the other was Beauty and the Beast.  However, it is mentioned that both actual worlds were destroyed, and the latter is visited in Kingdom Hearts II.