Bowser stage

A Bowser Stage is any of the three mini-stages where you fight Bowser. The three Bowser courses, in order, are Bowser in the Dark World, Bowser in the Fire Sea, and Bowser in the Sky.

The stages are all entered via holes in the ground in the castle, as opposed to paintings. All of them have a red coin star, and at the end they have a pipe that takes you to a sublevel where you fight Bowser.