Bowser in the Fire Sea is the second Bowser level in Super Mario 64. It can be accessed by going through the big star door in the basement, which requires 30 stars to open, and then collecting the star "Board Bowser's Sub" in Dire, Dire Docks.
Collecting the key from this level is mandatory to completing the game as there is no known way to enter the second floor of the castle without collecting it.
A Press Counts[]
This level requires one A press to complete in all versions of the game other than Wii Virtual Console (VC) and the Wii U's Wii mode's VC. This A press is to get past the pole in the level. The A press count doesn't change when collecting the 8 red coins.