Palawan Underground River or St. Paul Subterranean River

Longest Navigable Underground River in the World

This is the most famous cave in the Philippines. The longest underground river was discovered a few years back in Mexico somewhere in the Yucatan. St. Paul Underground River in Palawan, Philippines may not be the longest underground river in the world anymore, but it is still the world’s longest navigable underground river. The navigable part of the river inside the cave of the 4000-acre St. Paul Subterranean River stretches 15 kilometers in length (5 miles). St. Paul Cave is the 3rd deepest cave in the country.