Bowser's Keep, also called Bowser's Castle, is King Bowser's home and is always the final area Mario visits to rescue Princess Peach.
Shown in Super Mario Bros. 3 and Paper Mario: The Thousand-Year Door, it is found in the Dark Land.
In the Mario Kart series, this is one of the game courses.
In Super Mario RPG: Legend of the Seven Stars, the castle is stolen by Exor and Smithy at the beginning of the game and King Bowser joins Mario to get it back.
In Paper Mario, Bowser uses this castle to steal Peach's and lift it into the stratosphere after imprisoning the 7 Star Spirits and stealing the Star Rod, but Mario, with the help from party members Goombario, Kooper, Bombette, Parakarry, Bow, Watt, Sushie and Lakilester, manage to take back the Star Rod and save Princess Peach.