Puerto Princesa is the capital of the island province of Palawan, Philippines.

At over 8 km in length, the Puerto Princesa Subterranean River National Park is claimed to be the longest underground river in the world. With its crystalline waters and spectacular cave formations, the Underground River is possibly Puerto Princesa's most popular attraction. The site was also declared a UNESCO World Heritage site in 1999. The winding path of the river is navigable via small pumpboats that depart from Sabang Beach. Travel time from the city proper to Sabang is about 1.5 hours (This can take closer to 3.5 if you choose to ride in a Jeepney, since you have to wait while they deliver goods along the journey.) A permit is now necessary to visit the underground river and only available in Puerto Princesa, though an online system is in construction. As of December 2018, you can purchase the tickets in Sabang pier: if you do it yourself it will cost you around ₱600, if you do it through your accommodation they might overcharge you up to ₱1200. You can also ask if you can make the return trip trekking the park and the jungle: you will need to get a guide to do that but the experience is worth your time and money. 

- Wikivoyage