Imagine accidentally plunging 300 kilometers beneath the Earth’s surface? What would the journey look like? While it sounds farfetched that anyone would get to see so far below the Earth’s surface, two miners accidentally stumbled upon a mine shaft that led them into the depths. What they saw down below was breathtaking — and an undeniable scientific breakthrough.
In the year 2000, the Delgado Brothers, two Mexican miners trenching in the Naica Mines for Industrias Peñoles, happened to accidentally spelunk into what became known as one of the most famous and dangerous locations on Earth. It was an otherworldly sight.
Christian Science Monitor
The environment in the Cave of the Crystals is so toxic that a human would die within five minutes without proper equipment. Luckily, the miners were prepared to explore one of the most breathtaking locations on the planet. This marked the third cave in the Naica Mines, and it was completely filled with glittering formations.
National Geographic / Carsten Peters
The crystals were primarily Selenite formations. The largest crystal measured 12 meters long, 4 meters in diameter, and weighed more than 55 tons. Each one was cut perfectly — not by a jeweler, but by nature. But that’s not all that was down there.
The Naica Mines caves soon attracted the attention of NASA. In 2008 and 2009, NASA Astrobiology Institute director Penelope Boston Ventured into the Giant Crystal Cave. Boston was one of the scientists who discovered the crystals held a secret.
NASA Astrobiology Institute
They contained living organisms! The microbes found in some of the crystals were between 10,000 to 50,000 years old, and the crystals acted as a little incubator for what was growing inside. Talk about ancient!
But how could an area so beautiful also be so deadly to human life? Ironically, the answer lies in what allowed the microbes to grow in the first place: the extreme temperature, gasses, and the fact that the tunnels were actually once full of water.
The caves have been drained over time by Industrias Peñoles. Known primarily for their production of lead, as the mines went deeper, elements such as zinc, silver, and gold were discovered. This was one of the primary drives for the drainage of the Naica Mines.
In 1910, one of the first famous crystal rooms was discovered. The sharp-walled room earned the name “Cave of Swords.” Rooms entirely composed of crystals like these motivated Naica Mines to keep draining.
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There are three charted caves in the Naica, Mines. The deeper the tunnel, the hotter the water. The temperature changes in the water allowed different types of crystals to grow, including the ones holding ancient, yet living microbes. But what causes the temperature changes in the first place?
Underneath the waterfilled tunnels is a pocket of magma pushing towards the Earth’s surface. These heat levels allowed growth of microbes, but is deadly to humans, even when drained.
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The conditions of the famous Cave of Giant Crystals included temperatures of up to 138 degrees Fahrenheit and 100 percent humidity. If a person stayed down there too long, their lungs could fill with fluid, causing them to implode!
These intense conditions did not deter NASA scientists from continuing to explore the caves. Scientists were eager to find more life. In the end 40 strains of microbes were discovered, some of which were viruses.
Even stranger, these microbes had hardly any closely established terrestrial relatives. Their nearest relatives are 10 percent different in terms of genetics. Could this be alien life?
National Geographic by Carsten Peters
Unfortunately, the international attention caused damage to the mine. The areas of the caves that were tolerable to the ordinary person became tourist destination sites, and some greedy sightseers stole crystals. In 2010, it were closed to the public, but something was causing the crystals to rot.
Alexxander Van Driessche / PBS
Even though it was decided to shutter the mines, other variables played into the deterioration of the crystals. Excited to discover the next wonders, Industrias Peñoles looked to pump more water out of the tunnels.
Water continually refilled the caves, yet Industrias Peñoles wanted to keep pumping. This was not cost-effective for the company. In addition, this continual drainage played a major part to the Cave of Crystals’ rapid deterioration. Scientists raced to find a solution to prevent potentially devastating loss.
It became apparent that the perfect formation of the crystals was due in large part to the pocket of magma which heats the water flowing through the tunnels. The water allowed the magical crystal pillars not only to grow, but also to maintain their 500,000 year old existence.
In 2015, the Industrias Peñoles was ordered to close the mines. The company closed the entrance to the Giant Cave of Crystals, allowing water to flood the tunnels. Scientists hope that re-flooding the Naica Mines will help the structures naturally repair.
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There is no specified closure time for the mines. Seeing as how the most massive structures took 500,000 years to form, the reopening may not happen in our lifetime. Still, NASA scientists remain hopeful that the site can recover sooner.
Original NASA team members, particularly Paris Boston, deeply miss the monolithic pillars of glistening crystals. While she longs for another chance to visit her favorite place, she also understands the importance of allowing the once natural habitat to repair. Luckily, there are a handful of other caverns that rival this Mexican complex.
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Though it functioned as a salt mine for a thousand years, today the space is a tourist attraction that some call a “space-goth fantasy.” Extensive renovations in 2008 made it into one of the most bizarrely beautiful sights on Earth.
Guests can explore tunnels and balconies carved out of salt, or simply admire the cave walls lined with cylindrical lights. In stark contrast to its futuristic vibe, Salina Turda still houses some of the original mining equipment.
Flickr / Robert Anders
The ridges of Monte Castillo are stunning on their own, but the winding cave system within the mountain might be even more impressive. Archaeologists first explored the tunnels in 1903 and made a startling discovery.
The site contains the oldest-known cave paintings, a few of which date back to 40,000 years ago! The markings even include outlines of the painters’ hands, stenciled in the cave’s natural red pigments.
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Nowadays, classical music echoes throughout the stream and walkways of Zhaishan Tunnel. However, its creators had much less elegant intentions for it during the 1960s.
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The Chinese military originally built the underground passageway and barracks to house and move troops in secret. Exorbitant costs compelled the army to abandon the tunnel before the National Parks system took it over in 1997.
Tucked inside Ozark National Forest, this three-story system has wowed explorers since the 1930s. It’s considered a “living cave” since dripping water is still reforming the many rock structures.
This Yucatan peninsula location holds the distinction of being one of the longest underwater caverns in the world. Deep inside, divers have found the remains of a mastodon, as well as the oldest known human remains in the area.
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Spelunkers have gone nearly 300 yards down into this cavern but have yet to reach its deepest point — some think it might reach over 3 miles. Scientists suspect that early North Africans used to inhabit the caves as well.
A volcanic explosion from over a millennium ago forged this circular tunnel through the Icelandic mountains. Fortunately, the passage has cooled off in the following years.
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Aside from lichen, almost no life can survive inside the cavern. However, it has created mesmerizing ice formations and crystals. Tour guides shine colored lights through them to create a kaleidoscopic effect.
Just about everybody in the greater Dayton area knows about this tourist friendly cave, but it lives up to the hype. It’s home to the Crystal King, a free-hanging stalactite that spans nearly five feet.
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Visitors to this site can wade through a subterranean river while tropical fish zip by their legs. Notwithstanding the cave’s natural beauty, it also houses dark archaeological secrets.
The cave’s twists and turns hold shards of ancient Mayan pottery, as well as human skeletons. Based on their condition, these remains very well may have been sacrificial victims.
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History buffs will thank the New Deal’s Civilian Conservation Corps for the expansion of this Sunshine State Cave. Guests come from all over to witness its bouquets of limestone stalactites and stalagmites.
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This underwater river cuts through a Kiwi mountain pass and covers almost six football fields. However, explorers have to be careful not to enter during periods of heavy rain.
Still, any New Zealander will tell you the stream is worth the trip. Hikers can also enjoy massive rock formations and beautiful vistas, not to mention mass eel migrations during certain seasons.
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Long before its famous 1980 eruption, Mount St. Helens carved out this lava tube. It’s one of the longest passages of its kind, stretching out over approximately 2.5 miles.
This cave remained undiscovered until 1974, so it is untouched by vandalism or other human interference. However, the thousands of bats that roost there have known about it for some time now.
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This UNESCO World Heritage Site includes one of the largest underground canyons on Earth. Over 100,000 make the trek out to Škocjan each year, though the caves frequently have to close due to flooding.
Sure, maybe visiting a mine isn’t your typical idea of fun. But when you go over 300 yards down into the Wieliczka Salt Mine, you’ll realize it’s well worth the trip. The workers down there had an interesting way of passing the time underground…
They carved incredibly intricate designs and figures out of the rock salt! Given that Kraków began mining there in the 1200s, the workers had a ton of time to hone their craft and create a truly otherworldly sight.
Wieliczka actually produced table salt up until 2007. Now, it remains purely as a historical site, commemorating the incredible effort and artwork of the miners. Some top contemporary sculptors have also visited to contribute their talents. Of course, Kraków isn’t the only city hiding a massive secret — underground or otherwise.
16. Teotihuacan, Mexico: Just northeast of Mexico City lies a complex of colossal temples and pyramids. These are the ruins of Teotihuacan, once the greatest city in the Americas before its mysterious collapse in the sixth or seventh century.
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Archaeologists still have much to learn about this lost culture, but they have discovered a fascinating truth about the city’s layout: three key structures — the Pyramid of the Sun, Temple of the Moon, and Temple of Quetzalcoatl — follow a peculiar pattern.
Specifically, they line up with the stars in Orion’s belt! We have yet to figure how the Teotihuacans achieved this feat with rudimentary technology. However, historians guess that their purpose was to create a “City of the Gods” by making their home reflect the design of the heavens.
17. Paris, France: Without a doubt, the Eiffel Tower is one of the world’s most famous sights. Once visitors reach its top, however, they spend too much time enjoying the view to notice a secret hidden just a few feet away — just as the architect intended.
Ignoring the critics who hated his design, Gustave Eiffel knew the tower would be a national treasure. He felt so confident, in fact, that he wanted his own space to take in the vista and entertain like-minded intellectuals. So he built a small apartment!
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The apartment is out of use today, but guests can still peek in through the window. It contains much of its original furnishings, complete with mannequins of Eiffel and his good friend Thomas Edison.
Flickr / Serge Melki
18. Pohnpei, Micronesia: Over 30,000 people of all sorts of nationalities live on the isle of Pohnpei. However, none of them can claim to be part of the Saudeleur Dynasty that once ruled there. Their culture fell hundreds of years ago, though relics of their past still stand strong.
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The best record of Saudeleur glory is the ruined city of Nan Madol. With its stone walls sunken into canals, Nan Madol once gained a reputation as the Venice of the Pacific. These days, more people compare it to Atlantis.
Legend has it that a pair of wizards and a flying dragon created the city, and it’s a fitting story. For centuries the ruins have captivated visitors, including supernatural author H.P. Lovecraft, who set some of his works in Nan Madol.
19. New York City, New York: Most tourists don’t realize it, but the Big Apple’s real treasures are nowhere near the commercial bustle of Times Square. Roosevelt Island — a strip of land just to the east of Manhattan — holds one of the city’s eeriest buildings.
During the late 1800s, Renwick Hospital treated New Yorkers who fell victim to the smallpox outbreak. Its doctors abandoned it for a more modern facility years later. Though it crumbled and decayed, some interesting tenants moved right in.
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Enough felines moved into the hospital grounds that Renwick is now a wild cat sanctuary! They roam within the ramshackle hospital walls, while humans are seldom allowed to enter — bad news for anyone looking for an affordable New York City apartment.
20. Naours, France: Located just off the Somme river, the charming hamlet gives off every appearance of a quiet country town. But thanks to its role in World War I, Naours has some astonishing secrets lying just below its surface.
To protect themselves and civilians from enemy attacks, Allied forces dug out an entire underground city! Winding rock tunnels connect over 300 rooms, where the town waited out bombing raids and firefights.
If you visit Naours today, you can still see where Allied soldiers etched their names and other graffiti into the stone walls. They had little else to do while huddled together, but their efforts produced an astonishing historical monument.
Yahoo News / Francois Nascimbeni
21. Urfa, Turkey: In 1963, archaeologists came across a buried structure in the Anatolia region. Its towering pillars were impressive, but what really shocked the scientists was the site’s age. It appeared that this building dated back to the tenth millennium B.C.
By 1996, a German archaeologist named Klaus Schmidt began excavating the site, known as the Göbekli Tepe, in earnest. As he studied the layout and artifacts within, he came to believe that it was not a settlement, but a temple.
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His research suggested this may even be the oldest place of worship on Earth! With Schmidt’s passing in 2014, however, we may never know exactly who constructed the Göbekli Tepe or how they moved these massive stones.
22. Chattanooga, Tennessee: If you look closely at some of the buildings in downtown Chattanooga, you’ll notice some odd inconsistencies. For instance, is that the top of a window just inches above the sidewalk?
Atlas Obscura / Daniel Jackson
Surprisingly enough, there’s an entire underground city beneath Chattanooga! It follows the same grid of buildings and streets, and nobody is quite sure why it’s there. The documentation was likely lost years ago. Still, historians have a compelling theory.
Tennessee suffered a devastating flood in 1867. Chattanoogans, hoping to prevent further disasters, may have raised the street level by 15 feet. As a result, they abandoned entire rooms and buildings. Brave explorers can still go down and see the filled-in windows and tattered wallpaper.