Billionaires' superyachts are bigger, better, and have more on board than ever

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 Yachts

• Superyachts, 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.