The Underground River, also known as the Puerto Princesa Subterranean River, is located in the Philippines. It flows beneath a limestone karst mountain range and is part of the Puerto Princesa Subterranean River National Park, a UNESCO World Heritage Site. The river stretches approximately 8.2 kilometers and features stunning rock formations and diverse ecosystems. Visitors can take guided boat tours to explore the river's unique underground passages. The area is home to various species of flora and fauna, including bats and unique marine life. The Underground River is a popular tourist destination, attracting nature lovers and adventure seekers alike.