Deep underground on the island of Palawan in the Philippines lies the Puerto Princesa River. Both a UNESCO World Heritage Site and one of the ‘New 7 Wonders of Nature’, it’s the world’s longest navigable underground river and makes for an exciting experience in one of the Philippines’ most popular islands.

Here’s everything you need to know about exploring the Puerto Princesa Underground River.

Wait, an underground river? How is that possible?

Yep, that’s right. In fact, the river flows directly underneath the St Paul Mountain Range, found on the mid-western coast of Palawan. The river channeled its way through a series of vast chambers and caverns over millions of years ago.

The cave system stretches for a total of 24km underneath the mountains, and the river itself winds its way through 8.2km of it. Besides being one of the longest underground rivers in the world, the PPUR is also one of the very few that outflows directly to the sea.

Puerto Princesa Underground river entrance, Palawan, Philippines

The river and caves are home to complex eco-system that has adapted to living underground here over hundreds of years. Many of the animals in the caves are found only here, including certain types of giant spiders, crabs, fish and snakes, although bats and swallows are likely to be the only ones you’ll see.

Is it worth the trip?

Yes, absolutely. It's an otherworldly experience: imagine paddling through the dark in a small boat – the boatman’s headlamp the only light guiding your way – while the soft click-click of bats, chirps of swallows and the echoey drip, drip of water from the roof is your soundtrack. You glide through giant cavernous cathedrals, past mushroom-shaped rocks, in-between candle-like spindles of limestone and into some of the darkest reaches of the underbelly of the cave.

Tours only take visitors up to the 4km mark, but those wanting to apply for a special permit far enough in advance, can tour all 8.2 kilometres. This far into the cave, it’s so narrow that boats can’t pass and you have to swim between the rock walls.

Conquer your fears of small, dark spaces however, and you’ll be treated to the rare sights of waterfalls gushing through the cave walls, a unique 20 million-year-old fossil of a sirenia or manatee, and a tiny rock passage that leads into a vast room, carpeted from floor to ceiling in glimmering crystals.

Palawan underground river, Puerto Princesa, PhilippinesImage by paweesit on Flickr (CC BY-ND 2.0)

Even the journey to the cave itself is worth it: you’ll enjoy a scenic 20-minute boat ride across the sea, past towering limestone karsts and walk through the national park, home to monkeys swinging through the tree canopies and giant monitor lizards slinking their way through the undergrowth.

So how can I visit?

The jumping-off point is the small village of Sabang, located around 40km north of the capital of the island – Puerto Princesa. You can either choose to visit on a day-trip from the capital or stay in Sabang itself, which also has a lovely beach, a couple of luxury resorts and plenty of cheap beach huts for backpackers.

Everyone wanting to visit the underground river must apply for a permit to do so, and because of limited capacity and high demand, it’s best to book a few days in advance. You can either visit on an organised tour or arrange the permit and boat ride yourself, and pay for everything separately.

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OK, I'm sold. What do I need to know?

Tours from Puerto Princesa (around 1800 pesos per person) usually include transport to and from the PPUR, your permit, the boat ride, a guide and lunch. Those staying in the small village of Sabang can also book a tour (significantly cheaper as it won’t include van transfer or lunch) or buy their own permits at the office on the wharf. Permits are 250 pesos for adults and 150 pesos for children, plus there's an environmental fee of 40 pesos extra to pay per person. Your boat ride to and from the entrance to the park and audio device will also cost extra.

Helmets and life jackets are provided and must be worn for the duration of the tour (lasting around 45 minutes in total). Remember to keep your mouth closed when you look up, as the cave is also home to thousands of bats, who often drop "gifts" (read, faeces) from above.

Inside Puerto Princesa Underground River, cave system, the Philippines

An audio guide is available and provides lots of scientific information about the river and the caves, as well accompanying atmospheric music. Although informative, at times it’s also a little far-fetched, telling you to look out for rock formations that resemble Sharon Stone from Basic Instinct or Jesus at The Last Supper. If you don’t want to spend your time here looking around in bewilderment or getting frustrated when you can’t spot the formations, remove your earphones and let your imagination take over.

The author travelled with Corazon Travel, based in Puerto Princesa who charge 1840 pesos for a day tour to the Underground River.