‘Anahulu Cave Tongatapu

Tongatapu’s most famous cave is an over-loved, slightly eerie place full of stalactites and stalagmites, and blackened from the soot of flaming-frond torches and too much traffic. Inside is an underground freshwater pool where you can swim. The cave is managed by Teta Tours: if there's no one from the company on site, the generator won't be working and you'll be venturing into the inky void (not advised).