Bowser's Castle is a recurring location in the Mario series. It is the domicile of the Koopa villain Bowser and the base of operations for his army. The castle's name, design and greater location vary from game to game, but the castle is usually situated in a volcanic world and is characteristically an important base from which the Koopa King formulates his plans and summons his minions to take over the Mushroom Kingdom and carry out the capture of Princess Peach. Bowser's Castle is usually the final area that Mario and his friends visit to defeat Bowser and rescue Peach and is usually guarded by Bowser's most powerful minions. In the Mario spin-offs, the castle can serve as a go-kart course, a tennis court, a baseball stadium, etc., depending on the sport the game is based on.