Puerto-Princesa Subterranean River, underground river in the Philippines
The Puerto-Princesa Subterranean River flows directly into the sea and is framed by ancient limestone karst formations.
This park is a protected area of the Philippines since 1971 and was designated as a World Heritage Site in 1999.
It is also known as the St. Paul's Subterranean River National Park, named after the nearby St. Paul's Mountain Range.
Visitors can explore the underground river by paddleboat tours that traverse a portion of its length.
The river features a second floor, which means small waterfalls exist inside the cave system.
Sources: Wikimedia, OpenStreetMap