The Puerto Princesa Underground River is a UNESCO World Heritage Site located in the Philippines. It features a stunning limestone karst landscape and an extensive underground river that flows directly into the South China Sea. The river is approximately 8.2 kilometers long and is known for its impressive rock formations and diverse ecosystems. Visitors can explore the river through guided boat tours, which allow them to witness its unique geological features and rich biodiversity. The area surrounding the river is also home to the Puerto Princesa Subterranean River National Park, which protects various species of flora and fauna, making it a popular destination for eco-tourism.