Location: Niihau, Hawaii, USA
Purchased: $10,000*
Current Value: $171,460*

Niihau is a large inhabited island in Hawaii, measuring almost 70 square miles. The island is a hotbed for endangered species, including Brighamia insignis, which is a type of Hawaiian lobelioid, a flowering plant. In 1864, Elizabeth Sinclair, a Scottish plantation owner, bought the island for $10,000.

In the late 1800s, she passed ownership of the island to her descendants, the Robinson family, and they’ve owned it ever since. The Robinson family keeps the island private, refusing all outsiders except the U.S. Navy and other government officials and invited guests. Though there have been a few safaris and hunting tours, Bruce and Keith Robinson, the current owner-managers, keep a tight grip on the island.