The Underground River, also known as the Puerto Princesa Subterranean River National Park, is a UNESCO World Heritage Site located in the province of Palawan, Philippines. It's renowned for its stunning limestone karst landscape and its impressive underground river system.

The Underground River stretches for about 8.2 kilometres (5 miles) and is one of the longest navigable underground rivers in the world. However, only a portion of it, about 4.3 kilometres (2.7 miles), is open to tourists. Visitors typically embark on guided boat tours that take them deep into the cave, where they can marvel at the spectacular rock formations, stalactites, and stalagmites illuminated by spotlights.

Aside from its natural beauty, the Underground River is also home to a diverse ecosystem, including several endemic species of flora and fauna. It's a habitat for various wildlife, such as bats, swiftlets, and reptiles, making it not only a geological wonder but also an important ecological site.

To preserve its natural integrity and manage tourism sustainably, visitor access to the Underground River is regulated. Visitors need to secure permits and join guided tours organised by accredited operators. This helps minimise the impact of tourism on the delicate cave environment while ensuring that visitors can safely enjoy this extraordinary natural wonder.

Overall, the Underground River is a must-visit destination for travellers exploring Palawan, offering a unique and unforgettable experience of exploring an underground wonderland amid stunning natural surroundings.