Buoy Base Galaxy

The Buoy Base Galaxy is a galaxy that appears in Super Mario Galaxy. This galaxy appears as a large tower with a moat. To climb the tower, you had to release the weight from the bottom and to collect the Blue Star Pieces along with some other things (turning off the cannons and turning on the platforms). The Floating Fortress might refer to the planetoid above the tower, or it might refer to the Buoy Base itself.

Secret of Buoy Base
Mario has to collect 5 blue star chips to make a Pull Star so he can go to the Pokéball-like Planetoid so that Mario can collect the Green Power Star.