Subterranean Rivers—Water Flowing Underground

Off the midwestern coast of the Philippines sits Sabang, a small tropical beach village surrounded by jungle. From Sabang, a fifteen-minute boat ride or a short hike through the mountains will take you to the Puerto Princesa Subterranean River National Park. There, nestled amongst the mangrove forests and freshwater swamps, you’ll find the entrance to one of the longest underground rivers in the world. 

More intrepid travelers can venture another 3 kilometers—with a special permit, that is. But after that, the subterranean river remains unnavigable and yet-to-be explored.

The river starts in the nearby mountains but soon appears to vanish as it shifts course to flow beneath the Earth’s surface for a total of 8.2 kilometers (or about 5 miles). An average tourist can easily explore the first 1.5 kilometers of the river and the cave system it has helped to carve out via canoe and led by a guide with a flashlight. More intrepid travelers can venture another 3 kilometers—with a special permit, that is—to see more of the impressive cave-dwelling stalagmites and stalactites up close. But after that, the subterranean river remains unnavigable and yet-to-be explored. 

Even amongst underground rivers, the Puerto Princesa is unique. At its end, it flows directly into the sea, which leaves the end of the river subject to the influence of ocean tides. UNESCO has named the river a World Heritage Site and to protect it, only allows 600 people to visit per day. Such a unique habitat is also home to a unique and thriving range of flora and fauna including 800 plant species and animals like crabs, snakes, and bats that are found nowhere else on the planet. In 2017, a new species of Huntsman spider was found wedged in the cracks of the cave walls along the underground riverbanks of the Puerto Princesa. I can tell you from my experiences with surface-dwelling Huntsman spiders in Australia that they are large and move fast, but beyond scaring you out of your wits, they're relatively harmless. 

The Sistema Sac Actun, as the underground network is called using the Yucatec Mayan word for 'white cave,' stretches for 95 miles.

The Puerto Princesa was thought to be the longest underground river until 2007 when two underground rivers and cave systems...

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