The Puerto Princesa Subterranean River is the longest navigable underground river in the world, running 8.2 km beneath the karst limestone mountains of the Saint Paul Mountain Range before emptying directly into the South China Sea. The river has been a UNESCO World Heritage Site since 1999 and was named one of the New Seven Wonders of Nature in 2011.
Guided bangka boats take visitors about 4 km into the cave system, where the river opens into chambers of extraordinary scale — some large enough to contain a cathedral. The formations include towering stalagmites, delicate stalactites, and cathedral-like domes. Nesting swiftlets and cave-dwelling bats are everywhere; the guano creates a rich if pungent ecosystem.
The park is 80 km from Puerto Princesa city. You need a permit (bought in advance online or through a tour operator) and a seat on one of the bangka boats that enter the cave — numbers are strictly controlled. Reaching the cave involves either joining an organised tour or taking a van to Sabang and then a 20-minute boat ride to the park entrance. The path through the jungle from Sabang to the beach is worth walking in its own right.