5 Most Amazing Caves
By Julia Layton
While most of us like to think we're standing on solid ground, the reality is quite the contrary: The Earth just beneath our feet is kind of like Swiss cheese. It's riddled with holes, networks of them, carved into layers of stone by dripping water or eaten away by acid over millions of years. And when those holes have an opening at the surface of the Earth and are big enough for a human to climb into, they're called caves. Let's take a look at five of the most amazing caves out there. Each contains incredible features that make them noteworthy, and most of them are open to the public -- even to the nonspelunking public. 5. Carlsbad Caverns (United States) Carlsbad Caverns National Park New Mexico, United States A whole other world lies beneath the Guadalupe Mountains in Carlsbad, N.M. It took millions of years to produce the enormous underground rooms that draw visitors to Carlsbad Cavern National Park from around the world. With three known levels, at 750 feet (229 meters), 900 feet (274 meters) and 1,350 feet (411 meters) below ground, respectively, there's plenty for those visitors to experience [source: NPS]. The caverns seem decorated with some of the most stunning cave features around, including the Giant Dome, a column measuring 62 feet (19 meters) tall and 16 feet (5 meters) in diameter, and the Frozen Waterfall, a stone creation that bears an uncanny resemblance to its namesake [source: NPS]. There are stalagmites and stalactites of every shape and size, as well as basins lined with onyx crystals. And that's just what's been discovered so far: The caverns are still being explored and uncovered today. 4. Cave of Crystals (Mexico) Naica Mountain Naica, Mexico In Naica, Mexico, volcanic activity created conditions that would one day lead to an amazing discovery: A cave housing what may be the largest crystals in the world. Cueva de los Cristales, or the Cave of Crystals, is a natural marvel of cause and effect. A volcanic eruption built Naica Mountain, depositing tons of anhydrite, which is a high-temperature form of gypsum. Some have compared the sight to Superman's home -- mammoth, glittering crystals jutting out from every surface. But only a relative few have seen the Cave of Crystals up close. Discovered in 2000 by a couple of miners, Cueva de los Cristales is part of an active mine, and it gets so hot down there that the cave researchers and journalists who have gotten a peek have had to wear full protective gear. 3. Mammoth Cave (U.S.) Mammoth Cave National Park Kentucky, United States It took 10 million years for Kentucky's Green River to create Mammoth Cave, and it shows: Mammoth Cave lives up to its name. It's the longest known cave in the world, by far: Measuring approximately 360 miles (580 kilometers) long, it's four times longer than the second longest cave, Optimisticeskaya in the Ukraine [sources: NPS, GORP]. It's not just extreme in length, either. Mammoth Cave boasts some interesting life forms, like eyeless fish, shrimp and beetles as well as spiders with no pigmentation. There are tremendous columns, like the 192-foot (59-meter) Mammoth Dome, and rivers running through the lowest levels of the cave. Visitors to Mammoth Cave National Park in Kentucky can check out 10 miles (16 kilometers) of the extensive cave system. 2. Mulu Caves (Borneo) Mulu National Park Sarawak, Borneo On the island of Borneo, visitors can tour some of the biggest and longest cave passages in the world, all within a single cave system. The Mulu Caves beneath Mulu National Park were carved out of limestone over millions of years, and so far, 125 miles (200 kilometers) of underground cavern have been explored; it's possible there's three times that distance waiting to be discovered [source: FDSM]. The cave system offers tours for everyone from beginners to experienced spelunkers. Those looking for a real expert experience can attempt the 10 or so hours of total darkness required to navigate Sarawak Chamber. 1. Waitomo Glowworm Cave (New Zealand) Waitomo, New Zealand In New Zealand, music lovers can go underground to experience some of the most memorable performances. The Waitomo Glowworm Caves have hosted musical events due to the system's incredible acoustics. Specifically, the music venue is The Cathedral, a 60-foot-tall (18-meter) room on the cave's lower level that has hosted the likes of the Vienna Boys' Choir and Dame Kiri Te Kanawa [source: Discover Waitomo]. Its unique acoustics are said to produce an incredibly pure sound. But that's not actually what the caves are famous for. As the name implies, the Waitomo Glowworm Caves have their own indoor illumination: thousands of Arachnocampa luminosa glowworms. The mosquito-sized creatures are found only in New Zealand and cast a glow over the cave's interior. Visitors can particularly enjoy the glow during a boat trip down Waitomo River, which runs through the lower level of the cavern.