cocoon ,

The world of Cocoon floats in the sky above the world of Pulse in Final Fantasy XIII like a low-hanging moon, with a large piece taken out of it, giving a view of the hollow inside, where the inhabitants of Cocoon actually live, on the inside of the shell. It is a futuristic paradise protected by advanced technology against intruders from the planet below. It is ruled by the Sanctum and its army, PSICOM.
Cocoon is said to be built by the fal'Cie to protect humanity from the monster-infested Pulse. It contains futuristic cities, such as the capital city of Eden and the port city of Palumpolum, expansive highroads located in the Hanged Edge, and exotic jungles. There is also lake called Bilge located at the bottom parts of Cocoon. However, due to the fall of the Pulse fal'Cie, the water of the lake has been changed into a crystalline matter.