Don't let yourself be fooled. This isn't Bowser's Castle, but a part of the Mario Kart course with the same name.
Bowser's Castle is a castle residing in space sector 1337 of The Known Galaxy.
Actually, it is under construction now. Construction started in 1585 and the most possible date of construction's end is 10986.
Bowser's Castle Project was invented by unnamed Koopa Troopa, who was a farmer. Bowser and his army stopped near his farm one day and stole anything, that they could eat or sell. One of stolen things was a book with pictures of great castle, floating in space and fireing lazors in Mario's house. Bowser said that he loves pictures and send the book to his castle. Later he send koopas to Space Sector 1337 to build the Castle.
Bowser's Castle is the biggest weapon castle in history. Most of mass destruction weapons are in castle dungeons.
Bowser sometimes visits Bowser's Castle to decorate his throne room. It has been rumoured that George W. Bush and The scratch cat are hiding in the weapons warehouse, if seen please report to the koopa squadron -9.