Gate

Gates are essentialy Keyholes, only gates are another path between the worlds. Every world has a gate and keyhole, although some are still unknown. Just like keyholes, heartless can open gates and travel between worlds. In Kingdom Hearts, the keyholes were sealed, leaving no way to travel between each world. About a year later, the heartless found another method of travelling between worlds, the gates. A good portion of the gates are revelled in Kingdom Hearts II.

The gates are opened by the item in question (see below) is surrounded in light and then a huge gust of wind blows. The item in question becomes what looks like a keyhole and then Sora spins his keyblade and seals the gate. Sora, Donald and Goofy continue on their adventures there after.

It's likely that Worlds within worlds do not have gates, because the outer world's gate also serves as their own. This could be true for Space Paranoids, 100 Acre Wood, and Timeless River.

List of Gates

 * Twilight Town: The blue orb from the Struggle Trophy.
 * Hollow Bastion: The Hollow Bastion Restoration Committee honorary membership card given to Sora from Leon.
 * Land of Dragons: Shan-Yu's sword.
 * Beast's Castle: Beast's Rose.
 * Olympus Coliseum: The Olympus Stone. The stone is used to block out the negative energy when in the Underworld. (In game terms, it lets you use your Drive Form.)
 * Disney Castle: The Cornerstone of light. After you return from the Timeless River, Sora seals the Cornerstone of light.
 * Atlantica: A bubble.
 * Port Royal: Jack Sparrow's Compass.
 * Agrabah: A red diamond from the Cave of Wonders.
 * Halloween Town: Jack Skellington's Santa Claus costume.
 * Pride Lands: Mufasa's Ghost.
 * Realm of Darkness: The Sea-salt ice cream given by Riku.