Aldabra Islands sits in a far-flung corner of the Seychelles in the Indian Ocean. Though it remains relatively unknown, it is the second-largest coral atoll in the world. Aldabra has a huge population of giant tortoises (most estimates are around 100,000), but it does not have any permanent human residents. Arguably the most protected of all the islands on this list, Aldabra has long benefited from an impressive conservation effort. Conservationists have a history of fighting off attempts to build various military bases or permanent settlements on the island.