Secret Forest

The Secret Forest of Kingdom Hearts III is a special location where time does not matter. Merlin and the Three Good Fairies changed the flow of time there upon the request of Yen Sid, so time progresses faster inside the world's boundaries than it does elsewhere.

Settings and Areas
The Secret Forest is a vast and lush forest full of trees. The ground is covered in grass and clover. There's a clearing at the top of a cliff overlooking the setting sun shining on the forest, with a rock and a log across from each other, and a larger rock overlooking the edge.

Kingdom Hearts 3D: Dream Drop Distance
Yen Sid mentions to Mickey that Merlin and the Three Good Fairies are aiding Lea in a place that is temporally flexible, so he can learn to wield his Keyblade.

Kingdom Hearts III
Under Yen Sid's orders, Kairi joins Lea and Merlin to become a Keyblade wielder herself. There she writes Sora a letter she never intends to send.