Deep in the jungles of central Vietnam, there is a cave.
It’s called Hang Toi, or Dark Cave—and rightly so. With no artificial lights inside, it is simply six kilometers of pitch blackness. Instead of the usual limestone, it’s made mostly of basalt, a black volcanic rock, furthering the dark interior. First discovered in 1990, it’s the most popular tourist spot in Phong Nha-Ke Bang National Park. The area has hundreds of cave systems, but this is one you won’t want to miss. (Only if you’re up for an adventure, that is.)
Once you’ve paid the 450,000 VND entrance fee (about 20 USD), you get geared up. Personal items go into a locker, and the key is strapped to your arm. Wearing minimal clothes—you’re about to get muddy!—you climb a set of stairs to the top of a tower, where a park employee helps you into a harness and a hard hat.
Oh yes, this is more than just a visit to a cave.
A 400-meter zip line—the longest in Vietnam—deposits you just outside the cave entrance. The stunning blue-green water of the Chay River welcomes you in as you make the short swim to the opposite bank. Adrenaline pumps and eyes adjust as you enter the cool darkness.
Headlamps get switched on as a tour guide leads the group in, slowly and cautiously. With no artificial lights inside like most local caves, Dark Cave requires careful steps and a critical awareness. After a while, a large landing appears and the group takes a break to learn about the history of the cave. (While those with waterproof cameras or GoPros inevitably take selfies.)
Deeper and deeper the group descends. The darkness feels thick and impenetrable, and yet the lights from each person’s hard hats pave the way. The hard, dusty ground grows softer and softer the further in you go until the feeling of mud beneath your feet becomes impossible to ignore. The clay walls once solid and firm beneath grasping hands become slimy and gooey, and finally, you’ve arrived at the mud pit.
And this isn’t ordinary mud. This mud is buoyant.
What looks like melting chocolate ice cream is actually the consistency of a thick, creamy milkshake, and you cannot sink. Try as you might, you’ll hardly be able to put your feet down at the bottom, and everywhere you look people will be flopping down on the backs, only to appear to land in a jiggly, dark Jell-O. Even sitting down hard will make you feel as if you’ve landed on an invisible beanbag beneath the mud’s surface. Laughs and incredulous gasps will ring out as everyone becomes covered in a thick, sloppy mess, communally. It’s quite literally an underground mud bath, and your skin will thank you.
Pro tip: don’t wear anything light-colored, as it will inevitably be stained forever. And if you don’t want your bathing suit to smell forever, make sure to wash it straight after!
Finally, the tour guide convinces everyone to part ways with the mud, and the group jumps into the pitch black river that snakes its way through the cave, trying to rinse the far-reaching mud. The guide tells everyone to turn off their headlamps, and with a mix of hesitation and excitement everyone obeys, and suddenly you’re swimming through a river in a cave in total darkness. The group begrudgingly leaves the water and heads back towards the entrance, this time along a different route. What was once a straightforward walk through the cave becomes an obstacle course not for the weak of heart.
With the guide nonchalantly heading up the group, you’re led through passageways that become narrower and narrower, until finally, you come to caverns so small they require an army crawl flat on your belly. (This is when those hard hats come in handy!) Deep breaths and closed eyes get the most hesitant explorers through, and seeing the faint light from the cave entrance ahead invites a sigh of relief.
Finally, the group makes it back out and marvels at the wonder they’ve just experienced. Eyes must adjust once again, the sunlight feeling blinding. Shouts ring out as the next group begins to arrive via zip line, everyone chatty and excited about what’s to come.
The tour guide then shuttles everyone into kayaks, two to a boat, and the short distance back to the start is covered quickly. The adventure doesn’t end here though—Dark Cave is known not only for its cave but its water adventure sports as well. Another zipline looms over the sparkling water, this time with the option of releasing yourself into the river. Swing until the line stops, let go, and let the cool, crisp water wash over you. After trekking, crawling and shimmying through a cave full of mud, it’s impossible to decline. Groups do it over and over again until they’re finally spent, and head to the on-site restaurant to recover with some snacks and cold drinks.
The camaraderie that’s felt while experiencing Dark Cave makes it more than just a Vietnamese adventure. Southeast Asia has thousands of caves, and yet this one is special—visitors are literally underground in the middle of a jungle, covered in a thick brown mud, enveloped in pitch black air, amidst pitch black rocks. Everyone has to stick together, going at the same pace, and when the most claustrophobic of the bunch wants to turn back rather than crawl through an impossibly-small crevice, the group stops to urge them on. (Once you’ve laughed through an underground mud bath with strangers at the end of a cave in Vietnam, can you really be considered strangers anymore?)
You’ll see endless YouTube videos from adventurers that seem more like a creepy horror film than travel vlog, and once you’ve been through Dark Cave, you’ll understand why.
This is one cave you have to see to believe.
Suggested next reading: Hiking Into The Clouds With The Hill Tribes Of Northern Vietnam