The Philippines contains Puerto Princesa Subterranean River National Park, known for its navigable underground river.
The park lies on Palawan Island, about 80 kilometres north of Puerto Princesa City. Its principal feature is the Puerto Princesa Underground River, which flows through a limestone cave before reaching the South China Sea. Visitors commonly explore part of the cave by guided paddle boat.
The protected area was established as a national park in 1971 and became a UNESCO World Heritage Site in 1999. UNESCO highlights its karst landscape, underground river system, forests, wetlands, and coastal ecosystems. The cave includes large chambers and formations shaped by water over long periods.
The site is sometimes described as having one of the world’s longest navigable underground rivers, but it should not be confused with the longest underground river overall, a ranking that depends on definitions and measurement. The park is also one of the New7Wonders of Nature, announced in 2011.