Circuit Break Island

From the Super Mario Wiki

Circuit Break Island is an island Luigi visits to retrieve the third Marvelous Compass piece on his journey to rescue Princess Eclair. The residents of the island have kart races almost everyday, and the winner becomes king or queen of the island for twenty-four hours. However, these races are brutal. The karts race at high speeds are are equipped with missile launchers. It has never been seen, however Luigi mentions it in-between chapters during the events of Paper Mario: The Thousand-Year Door.

The only known kart is The Big Green 01.