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Cave of Swallows in Mexico
Located in the state of San Luis Potosí, Mexico, this pit cave is popular with ornithologists and adrenaline junkies. The former come to marvel at the clouds of birds—swifts to be exact—clinging to the cave walls, which also serve as breeding ground for parrots and parakeets. The latter base jump 330 meters down the perfectly vertical chamber to the guano-caked ground below. The view from the bottom is as daunting as it is feathered.
Fingal's Cave in Scotland
Fingal’s Cave, named for a mythic Scottish warrior, cuts through the tiny, uninhabited island of Staffa. The arched ceiling makes for some interesting acoustics, and the sound of rough waves battering the walls inspired German composer Felix Mendelssohn to pen an overture. The cave’s most striking feature is its Mordor-esque entrance, composed of hexagonal columns of basalt created by a process called columnar jointing, which takes place when lava cools and cracks. In spring and summer, the area around the cave is popular with both puffins and tourists.
Cave of Crystals in Mexico
Cuevas de las Cristales looks like something out of either a fairy—or cautionary—tale. Massive, perfectly symmetrical, crystalline formations cluster like iron filings, pouring out of the ground and walls in every direction. The crystals formed due to the cave’s position atop a magma chamber, which heated groundwater to create perfect conditions for suspended minerals to snap into place. The cave’s proximity to volcanic activity also makes it oppressively hot, warmer still at its lower depths. Temperatures exceed 110 degrees, and humidity approaches 100 percent, so spelunkers have to wear specialized cooling suits.
Waitomo Glowworm Caves in New Zealand
The glowworms that give the Waitomo Caves their celestial ceilings use their bioluminescence to lure flying insects into sticky, beaded strands of mucous. More relevant to humans, they look really cool. So does the 52-foot waterfall that still flows during heavy rain. Tours are available, though the number of visitors allowed in is dependent on air quality, temperature, and humidity readings taken with the glowworms’ health in mind.
Ellison's Cave in Georgia, USA
Caves are often measured by the structures they could hypothetically contain. Fantastic Pit in Ellison’s Cave, the deepest in the U.S., could engulf the Washington Monument. Plunging 586 feet beneath the surface of Pigeon Mountain in Georgia, the pit is open year-round but should only be entered by experienced climbers. At least three people have died of hypothermia after being trapped in the pit, and another fractured his skull and femur after plummeting 30 feet in 2013.
Deer Cave in Malaysia
Deer Cave in Malaysian Borneo was formed when freshwater eroded the limestone that also forms Gunung Mulu National Park’s famous karsts, jagged blades of rock jutting above the trees. The cave picked up its name from the animals that congregated near its opening to lick salt from the walls, but it is more commonly associated with bats, who stream out of the entrance daily. Visitors can reach the pit via a walkway that cuts through the canopy of the jungle, itself home to several types of monkeys and and more than 250 species of birds.
Lechuguilla Cave in New Mexico, USA
What sets Lechugailla Cave apart from others isn’t size but its diverse and pristine formations: shelfstones, calcite columns, cave pearls, soda straws, gypsum-frosted stalactites, and enough stalagmites to make the most jaded geologist swoon. Despite being known for years, Lechuguilla was largely ignored until cavers uncovered extensive passages in 1986. More than 136 miles of underground passages have been discovered since then, but only teams conducting scientific research and exploration are allowed to enter.
Son Doong Cave in Vietnam
Son Doong’s highest and widest portions extend more than 650 feet and 500 feet respectively, making it roughly twice the size of Deer Cave, the second-largest cavern in the world. It also remained undiscovered until 1991, when a local stumbled upon it while seeking shelter from a rainstorm. Aside from massive chambers and stalagmites, Son Doong offers something few other caverns can: a jungle. A portion of the cave’s ceiling has collapsed, creating an opening called a cenote, which allows light, along with plant and animal life, to creep inside. Explorers discovered Son Doong’s lush, sun-soaked “Garden of Edam” 2 two miles from the entrance and have since learned that this ecosystem within an ecosystem supports flying foxes, monkeys, and birds. The Vietnamese government is taking pains to keep the cave as pristine as possible, meaning access is restricted to only a couple hundred visitors this year.
Marble Caves in Chile
Most caves are made of limestone, a sedimentary rock that dissolves when exposed to the naturally occurring acids found in groundwater. Marble is actually made of limestone, formed by the heat and pressure of metamorphic processes that combine the stone’s calcite with impurities to create the colors, swirls, and patterns visible on your kitchen counter. The Cuevas de Marmol were carved out of a marble peninsula by a Patagonian glacial lake shared by Argentina and Chile. The entrances, which are on the Chilean side, are accessible by tour boats, but kayaks are also available and allow visitors to enjoy spectacular views of the Andes from the cave mouth.
Lake Superior Ice Caves in Wisconsin, USA
The ice caves that form along Wisconsin’s Apostle Islands National Lakeshore are only accessible by foot when Lake Superior is sufficiently frozen, and 2014 marks the first time in five years that conditions have been right. The caves have been a huge draw, with tens of thousands of visitors having already made the trek this year. After a short hike across the lake’s frozen surface, visitors are able to enter caves ringed by massive icy overhangs and filled with frozen stalactites. Lake Superior’s southern shore also happens to be one of the best places in the continental U.S. to view the aurora borealis, so those that brave the tundra at night may even be treated to a light show.
Orda Cave in Russia
Orda Cave is the world’s longest underwater gypsum cave. Its crystal clear water provides incredible views of its craggy paths and expansive chambers and makes the cave as dangerous as it is beautiful. The brittle gypsum that makes Orda so beautiful also makes it perilous, as chunks the size of cars frequently shear from the ceiling. Only experienced adventurers should brave its dangerously low temperatures and labyrinthine network of passageways.
Chauvet-Pont-d'Arc Cave in France
Chauvet Cave was rediscovered in 1994 after being concealed from prying eyes for more than 20,000 years. Featured in Werner Herzog’s memorable documentary Cave of Forgotten Dreams, Chauvet is home to the world’s oldest paintings and is the finest collection of Paleolithic art ever discovered. The cave is in astonishingly pristine condition, containing not only the touching and reverent depictions of our Ice Age forebearers’ natural world, but also physical traces of it. Tracks from cave bears extinct for thousands of years appear fresh, as do wolf prints accompanying those of a young boy.
Scientists learned their lesson after visitors’ breath caused mold to develop in nearby Lascaux, so it’s extremely difficult to enter Chauvet. However, a replica of the cave opened in 2015. You can also tour a virtual 3D capture of the cave online.
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