Deer Cave in Mulu National Park
Photograph by Robert Harding World Imagery/Getty Images
Two tiny figures look back towards the entrance of Deer Cave in Mulu National Park in the island of the Borneo's State of Sarawak. The pair is dwarfed by one of the world's largest known cave passages, 1.2 miles (1.9 kilometers) long, 500 feet (152 meters) wide, and 400 feet (122 meters) tall,. The massive cave system here draws explorers from all over the world-and is also home to much well-adapted wildlife. Deer Cave alone houses 3 million wrinkled-lipped freetail bats-whose droppings in turn feed countless dung-eating insects.
Lava Tube
Photograph by Patrick McFeeley
Steam rises from the Pacific as molten lava pours from the fiery interior of a lava tube near Kilauea, Hawaii. Lava tubes are created when lava flows through a channel for long periods of time, gradually building natural levees along its sides that eventually connect into an overlying roof. When lava flows stop, the caves may be left behind for exploration. Kilauea's tubes extend from the ocean to vents on the flank of the Pu'u 'O'o cone.
Ellison's Cave
Photograph by Michael Nichols
Their headlamps dimming in the distance, a group of cavers descends into Ellison's Cave far under Pigeon Mountain in northwest Georgia. The cave's "Fantastic Pit," seen here, is the deepest cave drop in the continental United States at a staggering 586 vertical feet (179 vertical meters).
Krubera Cave
Photograph by Stephen Alvarez
A caver rappels into the first pit of Krubera Cave in the Caucasus Mountains of Abkhazia, a politically disputed breakaway region of Georgia. Krubera is the deepest known cave in the entire world, delving more than 7,188 feet (2,191 meters) underground. Exploring it requires a kind of reverse mountaineering, as teams spend weeks moving from camp to camp while working their way even further into the Earth.
Hand of Dog stalagmite in Hang Son Doong Cave
Photograph by Peter Carsten
A spelunker takes a close look at the Hand of Dog stalagmite in Hang Son Doong Cave. The "Mountain River Cave", in a remote part of Vietnam's Annamite Mountains, was first explored in 2009 and boasts caverns large enough to hold a 747 airplane. In fact, though explorers have only scratched the cave's surface it may be the world's largest with continuous passages as wide as 300 feet (91 meters) stretching more than 600 feet (183 meters) high.
Kayaking Through Glacier Caves
Photograph by Doug Demarest
A sea kayaker cruises through a glacier cave carved out from among the giant icebergs of Resurrection Bay near Seward Alaska. Glacier caves are often created by the action of water on ice, though not all end up partially submerged as this iceberg example.
Waitomo Caves on New Zealand's North Island
Photograph by Paul Zahl
Boaters on an underground river enjoy a facsimile of the night sky created by a galaxy of glowworms on the roof of the Waitomo Caves on New Zealand's North Island. The tiny worms have become a rather large tourist attraction, and the caves they call home also boast notable stalactites, stalagmites, and interesting limestone rock formations.
Cave of Crystals in Naica, Mexico
Photograph by Peter Carston
A caver explores an otherworldly landscape in the aptly named Cave of Crystals in Naica, Mexico. The ice-cooled suit isn't just for show, the cave's 90 percent humidity and high temperatures (118 degrees Fahrenheit, 48 degrees Celsius) could kill a person in half an hour. The 36 foot-long (11 meter-long), 55-ton gypsum crystals here formed in hot, mineral-rich water that filled the cave until local mining operations pumped it dry. Should the mine close and pumping cease, the caves will refill and crystal growth will begin again.
"Snotties"
Photograph by Stephen Alvarez
A caver examines single-celled organisms, called "snotties," that produce a prodigious slime with a nasty kick-an acidic level rivaling battery acid. In Tabasco, Mexico's Cueva de Villa Luz these bacteria oxidize sulfur compounds that enter the cave from subterranean springs. Sulfur is the basis of nearly all life forms in this toxic-to-humans environment and cavers wear respirators for protection against sulfurous vapors.
Cave of Swallows
Photograph by Stephen Alvarez
Like spiders on silk, cavers begin an eye-popping descent into the Cave of Swallows, a Mexican open-air pit cave whose floor lies some more than 1,200 dizzying feet (366 meters) below-far enough to accommodate the Empire State Building. This free fall plunge is so exhilarating that it has become a major draw for adventure seekers including BASE jumpers. Animals have called it home for far longer and the cave takes its name from the many birds who nest in its vertical walls.
