The World’s Coolest Underground Wonders

This almost 800-foot-long limestone karst cave housed an impressive collection of stalactites and stalagmites even before they turned the lights on—more than 70 graffiti-like inscriptions date as far back as the Tang Dynasty (A.D. 792). But now, vividly awash in rainbow lights, it’s a Technicolor wonderland. Photograph away at formations anointed with poetic names such as Pines in the Snow, Dragon Pagoda, and Sky-Scraping Twin. The cave is an easy three miles northwest of Guilin and gets its name from the type of reeds that grew outside. guilintourist.com

Set along the eastern border of the Chapada Diamantina range near Andaraí in northeast Brazil, the Poço Encantado (Enchanted Well) is an underground lake with a natural window out to the Bahian jungle above. Between April and September, when the sun is at just the right spot in the sky, the light hitting the water in the cave turns it a deep, mysterious blue. The water is so clear that one can see more than 200 feet to the bottom, where ancient tree trunks and rock formations appear disorientingly close.

Joe Versus the Volcano this is not—no need for human sacrifice to see the inner chamber of Thrihnukagigur Volcano, which has been dormant for 4,000 years. Instead of erupting, the magma mysteriously drained away, leaving behind psychedelic mineral colorations geological geeks can gawk at today. After a hike across lava fields, visitors are whisked 390 feet into the volcano’s maw by a cable car. Tours usually occur between June and July, but can be extended beyond that period. insidethevolcano.com

Excavated by hand since the 13th century—although perhaps as early at 1075—the massive Turda Salt Mines in Transylvania is now a subterranean museum and recreation center with basketball hoops, a mini-golf course, Ferris wheel, and even an underground lake you can go boating on. From mine mouth to dome’s floor is a staggering 368 feet underground. Those with allergies and asthma will be especially interested in the mine’s halotherapy spa facilities, which use ionized air, pressure, and humidity in the salt-lined caves to treat persistent respiratory problems. salinaturda.eu

A UNESCO World Heritage site, this five-mile-long underground river lies beneath a limestone karst mountain on the island of Palawa, connecting the Cabayugan River’s flow to the South China Sea. The surrounding national park protects eight different forest systems, from mountains to beaches, and is a naturalist’s dream with a multitude of plant species (800 and counting) and vibrant animal life. While underground on guided rafting trips, visitors enter several large chambers, some as wide as 390 feet and almost 200 feet high, as well as passageways with a more claustrophobic fit. puerto-undergroundriver.com

La Cueva de los Cristales was discovered in the Naica Mine near Chihuahua in 2000 after water was pumped out of the 30-by-90-foot chamber, and there’s nothing else like it on—or under—earth. The crisscrossing gypsum columns are some of the world’s largest natural crystals. Despite its grandeur, visits are nearly impossible to come by due to dangerous conditions: near 100-percent humidity and temperatures as high as 136 degrees, warmed by a pool of magma sitting below the cave. There’s even been talk of refilling it with water. naica.com.mx

The real-life setting for a glow-in-the-dark sci-fi spectacular is two hours south of Auckland and the same distance west of Rotorua under Waitomo’s rolling green hills. Here caves are filled with arachnocampa luminosa (that’s New Zealand’s indigenous glowworms to you) that give off a subtle blue glow due to a chemical reaction occurring in their abdomen. Enjoy a boat ride that will take you through this galaxy of living lights, strong on sticky webs above. waitomo.com

Indulge in a little espionage while visiting the Allegheny Mountain’s posh Greenbrier resort, where a bunker was secretly built in 1956 to house members of Congress should nuclear war break out. Now declassified, the fallout shelter could have accommodated more than 1,100 people behind 25-ton blast doors; today, it’s a time capsule of Cold War hubris. The unused bunker came equipped with a power plant, decontamination chambers, communications equipment, meeting rooms, and a great hall for joint sessions—all over two football-field-size levels.

Uncover eons of religious belief at San Clemente Basilica, a 12th-century basilica built on top of a many-frescoed fourth-century church—itself built over a secular first-century home that stands next to a second-century temple used by an all-male fertility cult worshipping the sun god Mithras. Those with darker leanings can explore the Capuchin ossuary underneath the church of Santa Maria della Concezione, a 10-minute walk away, where the bones of 4,000 monks were used to artistically decorate the crypt in the form of chandeliers, coats of arms, and archways. Keep a lookout for a toddler’s skeleton turned flying grim reaper. basilicasanclemente.com

From 1906 to 1946, Sicilian immigrant Baldassare Forestiere built himself a subterranean home and garden modeled after the ancient catacombs of his homeland. The intrepid builder and gardener dug some 10,000 square feet of rooms, a chapel, and even an underground fishing pond using just farming tools. Forestiere’s 10-acre creation provides a cool respite from the scorching California sun, with blooming fruit trees reaching to skylights above.

Across the Atlantic, another secret underground bunker got a lot of use as the nerve center of the British war effort in World War II. Occupied by ministers, military personnel, and Prime Minister Winston Churchill from 1939 to 1945, the Cabinet War Rooms—part of the Churchill War Rooms museum—preserves many of the day-to-day artifacts used in that period, from large maps full of pinpricks indicating changing front lines down to the swivel chair Churchill used while presiding over the War Cabinet.

If the Apocalypse happens, this southern outback outpost will be ready: half of its 4,000 locals live underground, a vestige of a post-World War I opal mining boom that saw newly arrived solider-prospectors sleeping in dugouts. That and daytime temps in excess of 120 degrees. (Coober Pedy takes its name from the Aboriginal phrase for “white man in a hole.” Seriously.) Stay in an underground hotel and explore restaurants, art galleries, and a church, all below grade. Venture outdoors to play a round of grassless golf and see desert landscapes made famous in Mad Max Beyond Thunderdome and Pitch Black.

Each of Moscow’s Soviet-era metro stations hid a utilitarian function—World War II air-raid shelters—behind “palace-for-the-people” aesthetics, with Mayakovskaya’s richly Imperial elegance a boon amid the madness of the third-busiest subway system in the world. Columns lined with red marble and stainless steel, Romanesque arches, and dramatically lit mosaics create a surprisingly airy space more akin to a cathedral than to the windowless tunnel it really is. Walk through this station and exit through one of its six doorways right into the Tchaikovsky Concert Hall. engl.mosmetro.ru

Within a bare, black, isolated rock outcrop that towers 600 feet above the plain lies the largest and best-preserved cave-temple complex in Sri Lanka. Declared a UNESCO World Heritage Site, this sacred place offers 22 centuries of history to visitors. Pilgrims are treated to beautifully intricate mural paintings that cover entire cave walls and more than 150 statues of Buddha, other deities, and kings. A 100-foot-tall gold-plated Buddha at the entrance is the X that marks this treasured spot.

Set within Luxor’s Valley of the Kings, a final resting place for many of Egypt’s great kings, Seti I’s tomb is the largest and often viewed as the most impressive. (Tutankhamun who?) A recent excavation revealed it to be even bigger than originally thought, at 446 feet in length as opposed to 328 feet. Seti I’s tomb comprises several chambers covered with paintings and well-preserved bas-reliefs depicting the king’s introduction to the underworld, as well as scenes from the Book of the Dead, including a 52-foot-long rendering of the soul-eating snake Apep. sca-egypt.org

Built to shelter as many as 20,000 people—possibly by the Phrygians in eighth-century B.C. and expanded later by sixth-century B.C. Persians—Turkey’s largest and deepest underground city in the mountainous Cappadocia region is an ancient marvel with 18 levels dug more than 250 feet underground. It included homes, wine cellars, workshops, and chapels, plus room for livestock and access to fresh water. Beyond giant stone doors that could seal the city off from the outside, a maze of tunnels leads from one room to another, and, in some cases, another underground town miles away.

Depending which side of the war you were on, the 75-mile-long complex of tunnels could be a powerful symbol of human strength against adversity or a nightmare of guerilla tactics—either way, they’re incredible. The vast network reached almost to the Cambodian border more than 40 miles away and played a crucial part in the Viet Cong resistance. Visitors can reenact history and crawl through safer parts of the tunnels, see booby traps, and even sample a typical meal sequestered soldiers would have endured. An admittedly touristy day’s excursion from Ho Chi Minh City, but altogether fascinating. cuchitunnel.org.vn

On 1,375 square miles of desert 65 miles out of Las Vegas sit eerie ghost towns and a pock-mocked wasteland ravaged with nuclear bomb blasts, remnants of tests from the Cold War era up through the ’90s. But below ground are cavities sealed by the atomic infernos of some 828 tests that liquefied sand and rock into glasslike bubbles, unseen except when cave-ins leave craters above. Learn more on the science and history at the National Atomic Testing Museum, departure point for once-a-month public tours. National security clearance not needed, but book way in advance. nv.doe.gov

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Deep underneath Montparnasse lies a 200-mile network of Roman stone quarry tunnels turned macabre (though artfully arranged) resting ground for the remains of 6 million Parisians, including victims of the French revolution and perhaps even Marie Antoinette. The bones were exhumed from 1785 to 1860 to relieve fetid, overcrowded city cemeteries. Though much of Paris’s empire of the dead is beyond the reach of regular tourists, the catacombs have woven a spell over the more adventurous. Police once discovered one of the ossuary’s off-limits caverns being used as an illicit movie theater and bar-restaurant. catacombes.paris.fr

Crossing the Cowgate in Old Town Edinburgh, the South Street Bridge doesn’t seem like a bridge at all, seamlessly connecting two hills while hiding an underground world beneath. Eighteenth-century merchants set up storefronts at street level—some 31 feet above the actual ground—while 120 cramped, airless vaults below the viaduct first housed tradesmen (cobblers, smelters) before turning into a vice-ridden slum. Witness to murder, rape, kidnapping by devil-worshipping men, and even death by roasting, they’re now reputed to be one of the most haunted places in the world. visitscotland.com

Translated as the “Cathedral in the Mountain,” the barrel-vaulted Dom im Berg lies beneath Schlossberg, the Styrian capital’s Castle Hill, part of a system of tunnels dug out as air-raid shelters during World War II. Today you can take an elevator to the top or hang a right for the one-of-a-kind club and events space, where bodies gyrate regularly to the beat of electronic dance music under the heat of pulsating lights. Weird? Yes. Wonderful? Absolutely. spielstaetten.at

Follow the Reka River as it wends it way into a mountain through more than three miles of underground passages, deep chasms, underground lakes, and waterfalls. Though not quite as expansive as the mind-boggling Hang Son Doong in Vietnam, the world’s largest cave passage, the Škocjanske Jame ranks on UNESCO’s list of natural world heritage sites, primarily for its stepped limestone pools and an underground canyon that could fit a generous 45-story skyscraper—five stories more than even Hang Son Doong can handle. park-skocjanske-jame.si

Buried under an almost 30-story-tall funeral mound at the center of a city-size necropolis near Xi’an lies the Qinshihuang Mausoleum, remains of the first emperor of a united China, guarded by the incredible Terracotta Army—one of the world’s most visited ancient ruins. No two of the once brightly painted clay reproductions, modeled after real people, are alike—down to the armor, facial features, even hair and clothing, all standing with horses and weapons at his majesty’s command for thousands of years.

With an entrance a few feet from Hagia Sophia, the Basilica Cistern is an enchanting walk under a vaulted brick ceiling and through a forest of 336 mismatched Ionic and Corinthian marble columns (spoils of Constantine the Great), including two stone Medusa heads used as a base. Built by the Byzantine Emperor Justinian I, the royal reservoir could store up to 24 million gallons of water in a freshwater lake the size of two football fields.

The Cavern Suite claims to be the darkest and quietest motel room in the world, and it’s certainly vying for spookiest—with zero humidity, there’s no life in the cave but you (luckily it sleeps six). Located 220 feet below the surface, the room is fed fresh air from the Grand Canyon, 65 miles of limestone caves away. (Though it claims to be the deepest motel room, too, Sweden’s Sala Silvermine Underground Suite has it beat.) Design is retro-romp-room tacky, with 1970s Nat Geos as reading material. Look to China for more luxe digs when the five-star InterContinental Shimao Shanghai Wonderland opens in an old pit mine, with two underwater levels, in 2015. gccaverns.com