Once a notorious penal colony, Con Son and the other 15 islands of an obscure archipelago in the South China Sea, known collectively as Con Dao, might seem an unlikely destination for travelers. But their former off-limits status has preserved intact Vietnam’s most diverse offshore ecosystem.

Places of note: When not enjoying Con Dao’s rich biodiversity—including several endemic mammals, 44 unique plant species, and marine life spanning 270 different corals, giant clams, hawksbill sea turtles, and dugongs—travelers can take a glimpse of the region’s history with a tour around the Con Dao Museum and number of prisons that date back to the American and French colonial eras. The Hang Duong Cemetary, home to thousands of graves of war victims, also tells a powerful story of the the island’s past. From Con Son, a 30-minute speedboat ride takes one to the Bay Canh island, where a two and a half hour trek leads to the Bay Canh Lighthouse, which was built in 1883 and is one of the region’s most notable landmarks. Visitors looking to make the most of it all will want to book a stay at the Six Senses Con Dao, whose 50 sustainably designed timber- and-glass villas are sited along a great curve of empty beach five kilometers east of Con Son town.

When to visit: While the weather is driest from November through February, the waters are clearest from February to July, making it the perfect period for divers.

How to get there: The island is accessible using a 45-minute turboprop flight from Ho Chi Minh City.