Atlantica is a world that appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, and Kingdom Hearts II. It is based on the setting of the 1989 film, The Little Mermaid.
Almost completely underwater, Atlantica is a rocky world with immense holes on its surface. Beneath the surface is an entire world full of fish, merfolk, and other aquatic species that make up King Triton's underwater kingdom. The Heartless that appear in Atlantica are unique to it, such as Sea Neons which resemble jellyfish. In all games, the boss of Atlantica is Ursula (occasionally accompanied by Flotsam and Jetsam).
King Triton is the ruler of this world, and its Keyhole is hidden in Ariel's grotto. (more...)