The subterranean River or the Underground river is the most famous landmark in Puerto Princesa City. This subterranean river is the longest navigable river in the world. It features a limestone karst mountain landscape and many stalactites and stalagmites formations.
This river is approximately 8.2-kilometer, it is to be the longest navigable underground river in the world, the winds underneath was from the mountain range. The journey through the cave system alone is 24 kilometers long.
The entire area where the Underground River is located is actually a national park and a model of biodiversity. More than 800 plant species, about 300 trees, more than 195 bird species, 30 mammals, 19 reptiles, and eight bat species.