The Mushroom Kingdom.
The Mushroom Kingdom is the place where Mario, Luigi, Princess Peach, the Yoshies, Bowser, and many others live.
Bowser has attempted numerous times to conquer this kingdom, but his plans are always foiled by Mario.
Mario and Luigi: Superstar Saga[]
The Mushroom Kingdom played a minimal role in Mario and Luigi: Superstar Saga, as the player only began the game there. It is also revealed that a portion of Stardust Fields is part of the Mushroom Kindom's rule.
Mario and Luigi: Partners in Time[]
The Mushroom Kingdom plays a much larger role in Mario and Luigi: Partners in Time, but only the kingdom of the past. The only accessable region in the Present is Peach's Castle.
Mario and Luigi: Bowser's Inside Story[]
Bowser roams the Mushroom Kingdom during the events of Mario and Luigi: Bowser's Inside Story