World

A World is a location that appears in the Kingdom Hearts series. Most Worlds can be visited and are part of the game playthrough, although there are exceptions. Each World has its own distinct look, and for the most part hold true to the movies and cartoons they are based off of. As the Keyblade bearer, Sora is told not to meddle in the affairs of other Worlds, however, the disruption of the Heartless and the Nobodies force him to set things right.

World Characteristics
There are over 20 Worlds that have appeared in the series so far. Most of them are based on famous Disney films and contain locations and characters based on those movies. In certain worlds, a lead character from that area will be avaliable to fight, and can replace Donald or Goofy as a party member.

Eight Worlds are exclusives created by Square-Enix just for the Kingdom Hearts series, and are therefore not part of the Disney canon. They can have Square-Enix characters, especially from the Final Fantasy series, but will also have characters created just for Kingdom Hearts.

In addition, three Worlds can only be accessed by entering other Worlds:
 * 100 Acre Wood via Pooh's book in Traverse Town (Kingdom Hearts) and Hollow Bastion (Kingdom Hearts II)
 * Timeless River via the Hall of the Cornerstone in Disney Castle
 * Space Paranoids via Ansem's computer in Hollow Bastion.

For some Worlds, the name doesn't seem to accurately reflect what is found there. A famous example is Neverland in Kingdom Hearts; Sora and company get to go through Captain Hook's ship and fly around the Clock Tower, but never actually reach the island Neverland where Peter Pan and Tinkerbell live.

Travel
In Kingdom Hearts and Kingdom Hearts II, Sora, Donald, and Goofy use the Gummi Ship to travel between Worlds, an event that serves as a mini-game between areas. Some Worlds require certain special Gummi Blocks to access; for example, a special Navi Gummi must be created by Cid to unlock the second set of Worlds in Kingdom Hearts. Once open, the party can enter and depart each World through the Save Points scattered throughout each World.

In Kingdom Hearts: Chain of Memories, there are no Gummis; the Worlds Sora visits are recreations from his memories from the first game brought to life on each level of Castle Oblivion.

History
Prior to Kingdom Hearts, the worlds were separated by barriers, making it impossible for different worlds to communicate with each other. The arrival of the Heartless caused the barriers between the worlds to disappear, and some worlds were even consumed by the Heartless. Gummi Blocks are actually pieces of these broken barriers. The metaphysics of this prior to Kingdom Hearts is unknown, but will probably be revealed in Kingdom Hearts: Birth by Sleep.