Soul Calibur: Inferno's Stage I guess could be considered floating.

Sonic Adventure: The Egg Carrier

Doom: The entire third episode is an island floating over Hell.

Half Life: The entire Xen world is floating.

Super Mario Kart: Rainbow Road?

SaGa Frontier: The airship stages

Super Empire Strikes Back: The floating city where you have to rescue Han from that carbonizing thing.

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