When Virgin mogul Sir Richard Branson announced he'd paid $20 million to add Moskito Island in the British Virgins to his burgeoning tropical empire, he didn't mention the added value: a sunken treasure buried somewhere in its offshore reefs.

For decades, Moskito's resident eccentric was Bert Kilbride, a 92-year-old treasure hunter who calls himself the "last pirate of the Caribbean," shares Branson's penchant for exposed chest hair, and believes the shallows off Moskito may hold the elusive wreck of the San Ignacio, a Spanish galleon that sank nearby in 1742 carrying hundreds of pounds of gold bullion.

Perhaps the space-hopping mogul can use the underwater bank to offset the cost of solar panels: Like his nearby personal playground, Necker Island, he hopes to convert Moskito into a Balinese-style, "carbon-neutral" eco-retreat.