Hall of the Cornerstone

The Hall of the Cornerstone is a place in Disney Castle, and the holding place of the sacred Cornerstone of Light. It is located below ground, and the entrance lies beneath King Mickey's throne. Thanks to Merlin, it also holds the door to the world Timeless River.

In Kingdom Hearts II Final Mix, it plays a larger role, with Chip and Dale summoning the trio to the room. A portal opens, one that leads to the most enigmatic enemy to date: the Lingering Sentiment.

Trivia

 * In Kingdom Hearts II, when Maleficent begins to take Disney Castle with her dark magic, the hall is covered in thick, black thorns, similar to the ones surrounding Maleficent's castle in Sleeping Beauty and Hollow Bastion (where you fight Maleficent's Dragon Form).