Deep in the jungle of central Vietnam, there is a cave. It's called Hang Toi, or Dark Cave, and rightly so. With no artificial lights inside, there are simply six kilometers of total darkness. Instead of the usual limestone, it is made mostly of basalt, a black volcanic rock, which accentuates the darkness of the interior. First discovered in 1990, it is the most popular tourist spot in Phong Nha-Ke Bang National Park. The area has hundreds of cave systems, but this is one not to be missed. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay After paying the entrance fee of 450,000 VND (about 20 USD), you get ready. Personal items go in a locker and the key is tied to your arm. Wear minimal clothing: you're going to get muddy! - climb a flight of stairs to the top of a tower, where a park employee helps you put on a harness and helmet. Oh yes, this is more than just a visit to a cave. A 400 meter zip line - the longest in Vietnam - drops you off just outside the cave entrance. The beautiful blue-green waters of the Chay River welcome you as you take a short swim to the opposite bank. Adrenaline pumps and eyes adjust as you enter the cool darkness. Headlights come on as a tour guide leads the group inside, slowly and carefully. Without artificial lights inside like most local caves, the Dark Cave requires careful steps and critical awareness. After a while a large landing appears and the group takes a break to learn the history of the cave. The group descends deeper and deeper. The darkness seems thick and impenetrable, yet the lights from each person's helmets lead the way. The hard, dusty terrain becomes softer and softer as you progress, until the sensation of mud underfoot becomes impossible to ignore. The clay walls, once solid and firm under your hands, become slimy and sticky and, finally, you have arrived at the mud pit. And this is no ordinary mud. This mud is floating. What looks like melted chocolate ice cream actually has the consistency of a thick, creamy milkshake and you can't sink it. Try as you might, you'll hardly be able to get your feet to the bottom, and everywhere you look people will fall onto their backs, only to appear to land in dark, quivering jelly. Even sitting down hard will make you feel like you've landed on an invisible beanbag beneath the surface of the mud. Laughter and gasps of disbelief will ring out as everyone is covered in a thick, sloppy, community-wide mess. It's literally an underground mud bath and your skin will thank you. Pro tip: Don't wear anything light-colored, as it will inevitably be permanently stained. And if you don't want your swimsuit to stink forever, make sure to wash it right after! Eventually, the tour guide convinces everyone to part with the mud, and the group dives into the pitch-black river that meanders through the cave, trying to rinse off the mud that ran deep. The guide tells everyone to turn off their headlights and, with a mixture of hesitation and excitement, everyone obeys and suddenly you find yourself swimming across a river in a cave in total darkness. The group reluctantly leaves the water and heads back towards the entrance, this time along a different route. What was once a simple walk through the cave becomes an obstacle course not for the faint of heart. If you tend to be claustrophobic, Dark Cave is not for you. With your guide nonchalantly leading the group, you will be led through passages that become increasingly narrow,.