Monstro

Monstro is both a character and world from Kingdom Hearts. Like many of the worlds from the original game, it appears in Kingdom Hearts: Chain of Memories as well.

Though technically an interspace creature, an unbelievably large blue whale with man-eating tendencies, to be exact, it acts as a world in the first two Kingdom Hearts games, due to its massive size. Pinocchio's World, as of yet unnamed in the Kingdom Hearts universe, was destroyed, presumably by the Heartless.

Monstro is so enormous that its playable map is bigger than that of some worlds, like Wonderland. The boss inside Monstro is the Parasite Cage. The Watergleam Summon Gem is found within Monstro. If one leaves Monstro and tries to go to the different direction, then they will be caught by Monstro again and Monstro will appear twice on the map.

Story
While Sora, Donald, and Goofy were flying away from Agrabah to their next destination, they spotted something huge flying towards them on the Gummi Route. They quickly realized it was a massive whale, but were unable to get out of the way before the beast swallowed their ship whole.

Inside Monstro's flooded mouth, the trio met Pinocchio once more and his father Geppetto in a broken ship. It is never explained how Pinocchio managed to get from Traverse Town to Monstro. After speaking briefly with Geppetto, Sora ran after the puppet into the bowels of Monstro, where he quite quickly ran into Riku. The two friends exchange some quick words before Riku runs off with Pinocchio.

Sora chases the two all over the whale, until he eventually finds them in a large circuar chamber. Pinocchio is taken captive inside the Parasite Cage Heartless. Sora and Riku team up to take down the Heartless, but are unable to completely destroy it. Riku and the Heartless attempt to take Pinocchio's heart, but fail, and Riku flees as Sora enters the belly of the beast, literally, where he defeats the Parasite Cage once and for all.

From all the commotion in his organs, Montro spews out the Gummi ship and the trio to prevent any more trouble. Pinocchio and Geppetto also escape and set up a shop in Traverse Town.

Inside Monstro
The inner bowels of Monstro are an interconnecting maze. It takes a lot of patience and a little ingenuity to make your way all the way through. Many openings open into different parts of the same room, allowing for much confusion of anyone trying to work their way through. Many Heartless inhabit the different chambers of the tract. If the maze is correctly followed, it leads to the Bowels, where Parasite Cage is first fought.

The walls, floors, and ceilings of the many chambers are all identical - purple with multi-colored symbols and objects randomly scattered. In Chain of Memories, there are extensions coming out of the floor which can be hit or jumped on to gain items.

In the stomach, the floor is covered in acid, except the entry and the central platform where Parasite Cage sits. Platforms extend from the walls all around the stomach, allowing for an easier battle against the Heartless. It can only be reached by jumping up in the right area through the roof of the throat.

Other than the Mouth, Throat, Stomach, and Bowels, the ares within Monstro are all labeled as a numbered Chamber, rather than by a specific name, as they are in other worlds.