1) Caves form underground from water dissolving limestone over thousands of years, creating intricate mineral formations and unexpected environments. 2) Some of the largest and most fascinating caves can be found around the world, including Mammoth Cave in Kentucky which is over 500 km long, and caves containing massive selenite crystals in Mexico. 3) In addition to their geological features, caves have also been inhabited by humans and featured ancient cave cities, as well as modern establishments like luxury hotels carved within caves.

1. Caves: The World Beneath the World! If you are stretched and squeezed by everyday life, then you might be in perfect shape to explore caves. Enter a narrow natural passageway that may lead to simply mind-boggling underground world. Caves may lurk right under your feet: a fascinating and unexpected environment, which is often known only to spelunkers and dedicated Gollum-seekers.

2. Back to the Cave!

3. Gruta do Lago Azul, Bonito, Brazil. (photo by www.alexuchoa.com )

4. "Symphony of Stones" (how aptly named) - Garni caves in Armenia. (photo by eco culture)

5. Fairyland Cave Formations Caves are a fairyland of delight, from the burning hot enclaves to the glacial ice mazes. Thousands of years of dripping water, eroding stone and budding minerals create a silent world of mystery and beauty... Graceful arches, giant crystals... silent but for the sound of water dripping and bubbling through. A "Wishing Well" at Luray Caverns in Virginia (photo by Declan McCullagh)

6. One thing to keep in mind during cave exploration: though these structures are made of minerals, they are generally extremely thin and fragile, many of them are quite rare, and can be damaged or destroyed by touch alone. Calcite (the mineral which forms many cave structures), for example, is soft enough to be scratched by a fingernail. The most common type of caves form when slightly acidic rainwater trickles into the crevices of limestone and gradually widens the cracks as it dissolves the stone. Centuries of water, supersaturated with minerals, dripping from cave roofs cause stalagmites and stalactites to form (see here). (image via)

7. Some of the cave and rock formations: - Flowstone (also known as a Bacon formation) - Cave Pearls - Soda Straws - Helictites - Anthodites (or Aragonite) - Bottlebrush formation (image credit: Dave Bunnell)

8. Probably the most comprehensive cave-exploration site on the net is that of Dave Bunnell... You can spend hours there, wandering around pages, cataloging whimsical underground structures, oozing rock and dripping stone. (Gruta do Mimoso, Brazil)

10. (image credit: Alejocrux)

11. (image credit: Declan McCullagh)

12. One of the deepest known cave pits, Fantastic Pit in Georgia's Ellison's Cave descends 586 feet (179 meters) in a straight tunnel: (image credit: Michael Nichols, National Geographic)

13. Glacial Caves and Ice Caverns Some ice caves must rather be called "glacier caves", which can simply astound with the intensity of ice color: (image credit: Jenna and Tim Dickinson)

14. Here is a wonderful page of ice caves photography by Jason Gulley: (images credit: Jason Gulley)

15. No sign of Superman or Megatron there yet: Mount Kenya's Ice Cave Bobby Model, National Georgaphic)

16. Ice Cave in Matanuska Glacier, Alaska - photo by George F. Mobley, National Geographic

17. A lot of ice caves grow "hair" - ice extrusions, some are quite strange-looking: (image credit: Ian Mckenzie)

18. Brazil: Crystalline Underground Waters Mato Grosso do Sul region in Brazil (and especially the quiet town of Bonito) boasts many marvelous underground lakes: Gruta do Lago Azul, Gruta do Mimoso, Aquário Natural. Intricate limestone formations and grottos hide the intensely-colored pools and waterfalls (many adventure tours there feature diving, some pools are more than 100 meters deep):

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22. Limestone caves in the same region offer fantastic exploration:

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29. Venezuela: Cave of the Ghost Cueva del Fantasma is big enough for two helicopters to fly into it, but it's not technically a cave - rather, a collapsed gorge. It does, however, sport a huge waterfall right inside of it: (image via)

30. Iran: tremendous cave system Katale Khor is a cave dating back to the Jurassic period. It's one of the "snow caves" in the Southwest Zanjan province and connects to other caves - a huge underground infra-structure which can hide who knows what (definitely anti-American... wink wink). See more pictures here

32. (images credit: Ali Majdfar)

33. Vietnam: Hang Thien Cung cave There are plenty of caves in Vietnam, and just like in China, many are illuminated with garish colors. (see here). But sometimes even artificial light takes back stage to the incredible rock textures: (image credit: Tai Vo)

34. Mexico: Giant Selenite Crystals! In 2000, one of the most unusual and splendid caves was found in Mexico by miners. Located only a mile from an upthrust of magma, this cave is 112 degrees Farenheit and at 90-100% humidity, limiting greatly the amount of time explorers can spend in it. It is a spectacular cave, with gigantic crystal formations thought to be 600,000 years old .

36. (photos by Javier Trueba / Madrid Scientific Films, image via)

37. The crystals formed underwater; as water saturated with calcium sulfate heated in the cavern selenite molecules crystallized and grew, undisturbed, to giant proportions. The cave was drained (by unknowing miners) in the 1980's and stopped the process of growth. Who knows what we may find further on, in the heat and water? A description of one photographer's attempt to document this cave is here.

38. (images credit: Richard Fisher) "It is unquestionably magical that the cool white rays of moonlight can originate deep underground in a black chamber that is, at least in my perception, white hot." (Richard Fisher, photographer, comments on the huge selenite crystals.)

39. A Giant Geode Geodes are normally formed by volcanic or sedimentary geologic activity - a cavity in the rock is formed, inside which crystals begin to grow, such as amethyst, quartz or a number of others. Most geodes are small enough to fit in your hand, but this one is large enough to climb inside. The crystals found here are gypsum. (images credit: Javier Garcia-Guinea) The largest Geode Cave in US is located in Ohio: Crystal Cave, check it out.

40. Ancient Cave Cities Khosrov Caves in Armenia served as a shelter to ancient tribes - in a perfectly cinematic location:

41. (photos by Raffi Kojian and eco culture)

42. We wrote about Cappadocia cave city in Turkey before. But you might not be aware that more modern establishment makes its home there - a luxury hotel!

43. Considering how hot it can get outside, it definitely provides a welcome coolness: (images via)

44. This PC case mod would fit right there, in that cave hotel room: (case mod by Mashie)

45. Then again, there's a wildly original Stockholm subway station, seemingly built inside a natural (in reality - blasted) cave :

46. "Metro on Mars": (image credit: Hannes R.) More info : http://www.funonthenet.in/articles/caves.html

47. Documentation and text : Maria Angelica Lara Special thanks to: Werner D r echsler Compilation: Umane2006 THE END