Puerto Princesa Subterranean River National Park in Palawan lies in the Saint Paul Mountain Range, 81 kilometers (50 miles) from the center of Puerto Princesa City, but is still within the city boundaries. The Park is a natural wonder. Its geological features are unique and the Subterranean River is said to be among the longest in the world measuring up to 8.2 kilometers (5 miles).
Puerto Princesa Subterranean River is one of the few in the world that flow out into the sea from an inland source. It has been the focus of much curiosity and scientific investigation. The level of the freshwater river rises and falls with the tide up to a point of 4.3 kilometers (2.6 miles).
Puerto Princesa Subterranean River National Park consists of various landforms. The most impressive are the mountainous limestone plateaus, geologically called karsts, that form the rugged landscape of the Saint Paul Mountain Range with elevations ranging from sea level to a maximum height of 1,028 meters (3,372 feet). The topography of the property varies from flat plains to rolling hinterlands and hills to mountain peaks.
The extensive rainforest of the Park is the habitat of diverse endemic and endangered species of flora and fauna. The mouse deer, calamian deer, Palawan bearcat, porcupines, skunks, wild pigs, flying squirrels, rats, bats, and monkeys are among the animals that inhabit the Park. Cave-inhabiting forms of reptiles, birds, and mammals dominate the animals. All of these endemic to Palawan: they exist nowhere else on earth.