The Puerto Princesa Subterranean River in Palawan, Philippines, is a UNESCO World Heritage Site and one of the New7Wonders of Nature. This underground river flows through a spectacular limestone cave before emptying into the South China Sea. It's noted for its unique ecosystem, remarkable rock formations, and diverse wildlife, both within the cave and in the surrounding national park. Tours offer boat rides through its navigable portion, giving visitors a glimpse into this natural wonder.