Mario battling Bowser in the Bowser's Galaxy Reactor

Bowser's Galaxy Reactor is the final galaxy of Super Mario Galaxy. It is located at the center of the universe.

Like Gateway Galaxy, Bowser's Galaxy Reactor is not accessed by a dome. Instead, it is access by talking to Rosalina with enough stars on the Comet Observatory. The Comet Observatory will turn into its spaceship form and fly there. Mario must fight Bowser to save Princess Peach.