It's not the world's largest or most expensive yacht. It might be the most famous. Transformed from frigate to luxury vessel by Aristotle Onassis, the Christina O has played host to many notable names, among them Sir Winston Churchill and John F. Kennedy, who first met at the bar. It's capable of hosting up to 250 people at quay with accommodations for 34 spread across 17 cabins, and also has a mosaic swimming pool, three lounges, a deck dining area, spa, gym, and library. Fully refurbished in 2016-17, it's now available for charter.