The Puerto Princesa Subterranean River, a UNESCO World Heritage Site about 80 km north of the city, is the most famous single sight on Palawan. The river flows for more than eight kilometres entirely underground through a vast limestone cave system before emerging directly into the South China Sea — making it one of the longest navigable underground rivers in the world.
Visitors take a paddled banca about 1.5 km into the cave, with the guide pointing out limestone formations (the "Cathedral," the "Mushroom," the "Vegetable Market") that the lights pick out as bats and swiftlets wheel overhead. Numbers are now controlled by a daily quota; permits must be booked through a tour operator or the tourism office in Puerto Princesa days in advance.