Bowser's Galaxy Generator is the final level in the main story of the game Super Mario Galaxy 2. However, it is not the final level as there is a secret World S only accessible upon completing this level.
Bowser's Fortified Fortress
Mario crosses the entire fortress, dodging lava pits, fire balls, Banzai Bills, crushing walls, and many different types enemies in hopes are confronting Bowser for the final time. Upon reaching Bowser, the fight is played the same as the previous ones, only after his defeat, there is a part two in which Mario mush fling meteorites at Bowser while flying through space at what seems to be a very fast pace.