The Casino Royale, a 72-meter superyacht, exemplifies the feature-filled boats the uber-rich want to buy. She includes a private owner's jacuzzi, gym, sauna, steam room, and massage room.Courtesy of Tankoa YachtsSuperyachts, the most expensive asset a billionaire can own, are pushing the boundaries of luxury.The boats, which cost eight or nine figures, are getting larger and include more features than ever.From massage rooms to basketball courts, here's what the world's richest want on board.For many wealthy boat owners, a private spa is a must-have on board.