The Sleeping Keyholes (眠りの鍵穴, Nemuri no Kagiana?), also known as the Keyholes of Sleep, are seven unique Keyholes in the Sleeping Worlds. Like their counterparts in the Realm of Light, the Keyblade can interact with the Sleeping Keyholes by firing beams of light into them; however, that is where the similarity ends.
The location of a Sleeping Keyhole does not seem to be significant, as they often appear on nondescript walls, and Traverse Town's appears in the Fifth District, while its World Keyhole, the center of the world and its heart, is in the Second District. When a Sleeping Keyhole is unlocked, a large, almost circular section of the background behind it disappears with an effect reminiscent of shattering glass, revealing a torrent of gold energy and symbols underneath. This effect is also used when someone re-enters the Sleeping Worlds, as Sora does to thank the Spirits who helped him and Riku.
While the Heartless sought out the Keyholes of worlds to devour and plunge the world into darkness, the Dream Eaters seem unconcerned with the Sleeping Keyholes, instead focusing on attacking the worlds's inhabitants and generally causing mayhem. The known functions of the Sleeping Keyholes are to grant someone who unlocks all of them the power to awaken a sleeping heart, as well as freeing the Sleeping Worlds from their slumber. The Sleeping Keyholes may be indirectly related to the Princesses of Heart, as Yen Sid compares them when mentioning that as there are seven pure lights, there are seven Sleeping Keyholes.
Sleeping Keyholes Location
Kingdom Hearts 3D: Dream Drop Distance