Puerto Princesa Subterranean River

The world’s longest subterranean river, in the Puerto Princesa Subterranean River National Park, was recently voted one of the ‘New 7 Wonders of Nature’ – though it seems every natural wonder claims the title these days.

The flooded cave system stretches for 24km under the St. Paul Mountain Range on the island of Palawan; visitors can access the caverns above the water line by boat from the sea.

It’s a biodiversity hotspot too, with a rare full mountain-to-sea ecosystem. Giant spiders, crabs and snakes inhabit the cave, though in the near darkness all you are likely to see are bats. Highlights also include a 20 million-year-old fossil of a manatee.