The deep, dark world of caves is fascinating. From caves that light up with the glow of millions of glowworms, to underground caverns stuffed with crystals bigger than the average house -- here's our guide to 10 of the coolest caves in the world!
1. Cave of Crystals - Chihuahua, Mexico
Know what loves 99% humidity and a fierce heat that surges to 112 degrees Fahrenheit? That's right, crystals! Huge, glittering crystals -- the biggest in the world -- were found under the Naica silver and lead mines in Chihuahua, Mexico, by two amazed miner brothers in 2000. Heat and humidity might be the perfect environment for crystals... not so much for humans. More than ten minutes spent in this underground crystal forest can be perilous for anything not made of magma and gypsum.
2. Marble Caves - Patagonia, Chile
What's the biggest repository of marble in the world? We'll give you a hint: it's not the Taj Mahal. In fact, the world's biggest store of marble is to be found in a huge lake hidden deep among the Patagonian Andes. Among the soothing, glacial waters of Chile's General Carrera lake lies a whopping 5,000 million tons of marble!
Getting there? That's no mean feat: From the Chilean capital of Santiago, you'll need to fly 800 miles south to the city of Coyhaique. After that, it's another 200-miles' drive into the Patagonian wilderness, followed by a boat ride to get up-close to the caves. We think it's worth the trip: surrounded by the Andes and towered over by 6,000-year-old marble columns, caves and monoliths, it's impossible not to say, "Wow."
3. Sassi di Matera - Matera, Southern Italy
At least 9,000 years ago, our ancestors were dwelling in the honeycomb-like caverns of Matera in southern Italy. By the 1920s, the Sassi di Matera were causing a national outcry among concerned Italians: at a time when Fitzgerald was writing The Great Gatsby and Hemingway was dancing in the streets of Paris, over 20,000 landless peasants were barely surviving in these caves -- no heat, light or sanitation -- just malaria and malnutrition as bedfellows. In a tale of high-speed gentrification, the destitute were taken to new and improved housing, and today the dwellings are home to boutique hotels and chichi restaurants.
4. Skaftafell Ice Caves, Iceland
A photographer's dream, Skaftafell's ice caves are located on the frozen lagoon of Svínafellsjökull glacier -- the largest in Europe. The coolest thing about being in one of these caves? All the cracks, bangs and wallows crashing around you! Don't worry: The cave isn't about to collapse on your head. Whenever the glacier moves even by a millimeter, it causes the ice caves to move and moan along with it. Have fun!
5. Waitomo Glowworm Caves - North Island, New Zealand
Ah, New Zealand. Home to 3 million people, 60 million sheep, and even more glowworms! At Waitomo Caves, board a boat and cruise its eerie waters. As your eyes adjust to the dark, you'll see a Milky Way of stars light up the dark. Except they're not stars, they're... you've got it, glowworms.
Did you know that glowworms aren't actually worms? Rather, they're the fishermen of the gnat world, producing long glowing threads made of mucus and silk. Midges and insects are mesmerized by the light, and dance towards their ethereal flicker. The glowworms draw in their home-made fishing lines and enjoy the tasty snacks attached to the end. Yum.
6. Lascaux Cave - Dordogne, France
Before the Pyramids and Stonehenge, Machu Picchu and Angkor Wat - there was Lascaux Cave. Painted more than 15,000 years ago, the famous cave is covered with over 2,000 images of bison, mammoths and horses in visceral blacks, purples, reds and yellows.
When there were such pressing Prehistoric matters as hunting and gathering to do, it's unknown why a tiny group of early Homo Sapiens took the time to paint these images that, under flickering candle light, seem to move and shimmer. Some say it was to chart the stars, others say the cave paintings are representations of visions that came during bouts of prehistoric trance dancing.
Whatever their reason, the paintings are impressive. After Picasso visited Lascaux he is said to have remarked, "We have invented nothing."
Today, it's not possible to visit the original Lascaux Caves, because human breath and body heat damage the artworks. Instead, you can visit the exact replica at Lascaux II just down the road, or head to the Dordogne's Grotte de Font-de-Gaume for original prehistoric art.
7. Caves of the Thousand Buddhas - Gansu Province, Western China
Along the old Silk Road in the Chinese province of Gansu, the Caves of the Thousand Buddhas hold some of the most impressive Buddhist art in the world. Over 2,000 religious sculptures have been carved from the walls of over 400 caves spanning five floors.
What makes the caves so interesting is that it's possible to trace the early development of globalization in them. Artworks from the 5th century onwards show how the Buddhists were influenced by Greek, Persian and Indian culture, brought to the desert sands by early merchants traversing the Silk Road. Who would have thought that some caves hidden under the lonely sands could turn out so cosmopolitan?
8. Krubera Cave, Abkhazia Territory
Jules Verne's "Journey to the Center of the Earth" almost comes true at Krubera Cave, the deepest cave on Earth. Plunging 2,191 meters into the Arabika Massif, the intrepid explorers who have taken the plunge into record-breaking Krubera say it's like climbing an inverted Everest.
Explorers have to create base camps at different depths. At these camps they cook, sleep five or six to a tent, and huddle together for warmth. Taking about 14 days to reach the cave's end, one 300 feet-long passage is charmingly named "Way to the Dream." For people who suffer from claustrophobia though, such a narrow channel might seem like more of a nightmare, especially considering all the spiders, scorpions and amphipods hidden among Krubera's dark layers!
9. Benagil Sea Cave - Algarve, Portugal
Loved by a thousand Pinterest daydreamers, you've probably seen pictures of Benagil sea cave before. To get to the iconic cave in the Algarve, you'll have to charter a local fishing boat, but we think the trip is well worth it.
10. Eisriesenwelt Ice Caves - Werfen, Austria
German for "The World of Ice Giants," at over 42 kilometers long, Eisriesenwelt is the biggest ice cave in the world. Buried deep in the Austrian Alps, before its discovery by natural scientist Anton Posselt, locals were too scared to go inside the cave for fear it was the entrance to Hell itself. To us, its natural ice sculptures are simply beautiful.
-Contributed by Alisa Ross for Viator