Super Mario Kart
Bowser Castle 2 first appears in Super Mario Kart for the Flower Cup. It has Thwomps, and you have to hop over lava or you'll fall in it.
Mario Kart: Super Circuit
It appears in Mario Kart: Super Circuit as a new course in the Flower Cup and in the retro courses of Super Mario Kart. The new Bowser Castle 2 starts off with a boost pad and you pass a Thwomp. You then hop over lava with boost lifters. Then you pass by another Thwomp and you find several more boost pads and Podoboos.
Mario Kart DS
It appears as a retro course in Mario Kart DS as the third course in the Banana Cup.