Aldabra

It was declared a special reserve in 1981 after years of international scientific campaigning to stop a British military plan to build an airbase on the atoll in the 1960s, which was finally cancelled under pressure from bodies such as the Royal Society, so saving one of the best-preserved island ecosystems on the planet. It is the second largest raised coral atoll in the world and holds the largest population of giant tortoises anywhere, with over 100,000 animals — more even than the Galápagos. Its extreme isolation, more than a thousand kilometres from the main island of Mahé and reachable only with a special permit and several days by boat, has also preserved the Aldabra rail, the last flightless bird surviving in the western Indian Ocean after all its related species died out on other islands in the region.