The Puerto Princesa Subterranean River National Park is located about 50 km north of the city of Puerto Princesa, Palawan, Philippines. It features a limestone karst mountain landscape with an 8.2 km. navigable underground river. A distinguishing feature of the river is that it winds through a cave before flowing directly into the South China Sea.
It includes major formations of stalactites and stalagmites, and several large chambers. The lower portion of the river is subject to tidal influences. The underground river is reputed to be the world's longest. At the mouth of the cave, a clear lagoon is framed by ancient trees growing right to the water's edge. Monkeys, large monitor lizards, and squirrels find their niche on the beach near the cave.