WORLD
The technology is generally Industrial Age/turn of the century influenced, with added elements of magic and more advanced technology (i.e. zeppelins, guns, etc.). Instead of visiting different worlds, there are various continents both floating and on the world beneath, all of them isolated for several hundred years by the world's terrible storms. As far as is known, the ground and ocean beneath the thick layer of mist is uninhabitable and nothing can live there.

In truth, beneath the mist lies the dark side of the world, filled with all sorts of unpleasant creatures and every city that ever fell to the Heartless.
( More on his application. )