Super Mario Galaxy/Bowser's Star Reactor

Bowser's Star Reactor is accessible from the Fountain observation dome. You need 15 Stars to enter.

Star 1: The Fiery Stronghold
Follow the course round until you reach Bowser, a boss fight. Avoid Bowser's jump attack, the blue radiating shock waves, and the fireballs he breathes at you. Replenish you health with coins trapped in crystal and embedded in the ground (fire Star Bits to release the latter). Bowser will try and jump on you, so use that to make him jump onto the circular glass areas. These areas will break, causing Bowser to burn his tail on the lava and start running. While he is burning, spin attack him a couple of times. Repeat the procedure two more times.

Did you find?

 * 1-Up Mushroom trapped in crystal.
 * 1-Up Mushroom on lower-left of circular flaming platform.
 * Life Mushroom trapped in crystal during the collapsing floor sequence.