Nafsika Island, Greece
At 1,235 acres (500 hectares), Nafsika Island is not only one of the last undeveloped islands in the Ionian Sea in the Mediterranean, but also one of the largest [source: Private Islands Online]. Nafsika is right next to the Onassis family's Skorpios Island, and its price tag of approximately $10 million for such a large parcel begins to sound like a bargain compared with that much smaller island's estimated $200 million value. With lush vegetation, high mountains and 360-degree views, Nafsika would be the perfect location for a resort or a private retreat [source: Private Islands Online]. The island offers several harbors and protected bays ideal for docking a yacht, but there's one thing it actually doesn't have: white sandy beaches [source: Private Islands Inc.].