Monstro

Monstro the Whale is a character and world from Kingdom Hearts and Kingdom Hearts: Chain of Memories.

Monstro, though technically not a world, acts like a world in the first two Kingdom Hearts games. Monstro the Whale was the villain of Pinocchio.

Monstro is a whale, and so requires water. However, he apparently can survive in space, as he devours the Gummi Ship on their way to Atlantica. Monstro is so enormous that its playable map is bigger than that of some worlds, like Wonderland. Based on this, it may be surmised that Pinocchio's world, which was destroyed along with the Pride Lands and other worlds, is humongous and possibly as big as the World that Never Was (or bigger). Monstro was small in the movie, of course, compared to the ocean and the land.

The boss of Monstro is the Parasite Cage.

Trivia

 * The idea of Monstro's stomach being a level is probably based on The Legend of Zelda: Ocarina of Time, in which the belly of a giant fish was an entire dungeon.