Fusion City is the world's only surviving megacity. A colossal, domed city built in three levels, housing over a hundred million people.
Vault of Life
Level 0, better known as "The Vault of Life", is the subterranean level of Fusion City, housing all the maintenance systems to keep the city running.
Level 1 is what used to be the metropolis of D'jathla before the dome was built and as such it is very reminiscent of the cities of old.