Outstanding caves around the world
Here are selected some of the most surprising and interesting caves of the the world, arranged by the part of the world and in an alphabetic order.
- Cave of Altamira – Cantabria, Spain. Cave with some of the best cave paintings in the world, mostly polychrome paintings of wild mammals, 18 – 14 thousand years old.
- Chauvet Cave – Ardèche, France. Cave contains the oldest known cave paintings in world, made 33 – 30 thousand years ago. In hundreds of drawings shown at least 13 species of animals, artistic quality of paintings is very high.
- Cosquer Cave – Bouches-du-Rhône, France. Cave with Palaeolithic paintings. The entrance in this cave is located 37 metres under the sea level and most of the art has been destroyed by the sea. Still some 150 paintings remain, part of drawings is 27,000 years old and part – 19,000 years old.
- Daveli’s Cave – Athens, Greece. Since ancient times cave by the followers of Pan and nymphs is used as a worship site. Nowadays popular due to reported paranormal phenomenons.
- Eisriesenwelt – Salzburg, Austria. The largest ice cave in the world. Cave is more than 42 km long but the beautiful ice formations are at the first kilometer of the cave, at the entrance.
- Għar Dalam – Southern Region, Malta. Cave contains unique remnants of such animals as dwarf elephant, hipopotamus, deer and others, trapped on the island at the end of ice age, as well as the oldest human remnants in Malta (7,400 years). Cave paintings include paintings of elephants.
- Hohle Fels – Baden-Württemberg, Germany. Contains archaeological artefacts of world importance, including the oldest sculpture in the world: 35 – 40 thousand years old "Venus of Hohle Fels" as well as 35 thousand years old bone flutes – some of the oldest musical instruments in world. Remnants of cave bears, mammoths and other animals.
- Shulgantash (Kapova Cave) – Republic of Bashkortostan, Russia. Unique Paleolithic paintings.
- La Marche – Vienne, France. Cave contains 15,000 years old paintings of humans. Drawings are realistic to such an extent (f.e. showing individual people in great detail) that for long time this discovery was considered to be fake.
- Lascaux – Dordogne, France. One of the most important cave art monuments in world, containing beautiful paintings of animals and humans, some 16,000 years old.
- Movile Cave – Constanţa County, Romania. Unique cave ecosystem consisting of 48 species. 33 species are found only in this cave. Ecosystem of this cave was isolated from the outer world for 5.5 million years and air inside the cave has a different chemical composition.
- Ochtinská Aragonite Cave – Košice, Slovakia. The best known aragonite cave which is covered with very unusual crystals. Cave is only 300 m long.
- Optymistychna Cave – Ternopil, Ukraine. Fifth longest cave in the world and the longest gypsum cave in world. Total length: 257 km.
- Sistem Postojna-Planina – Inner Carniola, Slovenia. Roughly 25 km long cave system, recognized as the most biodiverse cave system in the world with 84 species of animals (mostly insects).
- Psychro Cave – Crete, Greece. Sacred Minoan cave with beautiful cave formations. Numerous artifacts found, including huge amount of semi-precious stones.
- Škocjan caves – Slovenian Littoral, Slovenia. Cave system with numerous unique characteristics: giant, 146 metres deep underground canyon of River Reka, underground travertine terraces, Bronze Age and later temples and Prechristian pilgrimage centre.
- Peştera Urşilor – Bihor County, Romania. Beautiful cave with remnants of some 140 cave bears (Ursus spelaeus) trapped by rock slide more than 15,000 years ago.
- Velebit Caves – Lika-Senj, Croatia. In one of the caves, Lukina Jama, there is the highest unhindered single drop in the world (513 metres). Contains also 553 metres deep pitch – the second deepest in the world. Enormous colony of subterranean leeches.
- Víðgelmir – Borgarfjörður, Iceland. Largest (by volume) lava tube cave in the world. 1,585 meters long cave contains ice formations, evidence of habitation, possibly from the Viking Age.
- Vrtiglavica (Vrtoglavica) – Slovenian Littoral, Slovenia. 643 m deep cave, which sontains the deepest pitch (single vertical drop) in the world (603 meters). 400 – 440 m tall waterfall inside.
- Bhimbetka rock shelters – Madhya Pradesh, India. Group of caves containing rich collection of cave art, up to 9,000 years old. Some of caves have been inhabited for more than 100,000 years.
- Dragon Hole – South China Sea, Paracel Islands. World’s deepest known undersea sinkhole, 300.89 m deep.
- Edakkal Caves – Kerala, India. Cave with unusual archaeological monument: 6 – 8 thousand years old petroglyphs which resemble ancient writing.
- Gomantong Caves – Sabah, Malaysia. Well known due to swiftlet nests which are collected in 90 metre height for bird’s nest soups. Enormous colonies of bats, dung beetles, centipedes and cocroaches.
- Gua Air Jernih (The Clearwater System) – Sarawak, Malaysia. The second longest cave in Asia, total length: 227 km.
- Gua Nasib Bagus with Sarawak Chamber – Sarawak, Malaysia. Contains the largest known underground chamber in the world which is some 700 metres long, 396 metres wide and 70 metres high.
- Ignateva Cave – Chelyabinsk Oblast, Russia. Limestone cave with unique archaeological finds including Venus figurine with 28 red dots between her legs (representing menstrual cycle), 6 – 8 thousand years old cave paintings.
- Jeita Grotto – Mount Lebanon Governorate, Lebanon. Beautiful, 10,050 m long cave with the world’s largest stalactite – 8.2 metres long. Includes 800 m long cave lake.
- Khoun Xe Cave – Khammouan, Laos. 13,6 km long cave, traversed by the largest cave river in the world. Here are located the largest rimstone pools in the world and here live the largest spiders in the world.
- Krubera Cave (Voronya Cave) – Gagra, Abkhazia, Georgia. Deepest known cave in the world, 2,197 meters deep.
- Liang Bua – Flores, East Nusa Tenggara, Indonesia. In the cave (and only here) there were discovered remnants of a newly discovered, extinct species of human – Homo floresiensis.
- Majlis al Jinn – Sharquiah, Oman. Ninth largest cave chamber in world in unique setting, available only by abseiling 118 – 158 meters through the ceiling. People live on the top of this enormous chamber which has only 40 meters thick ceiling.
- Paradise Cave (Dong Thien Duong), Phong Nha Cave and Son Doong Cave – North Central Coast, Vietnam. Some of the most beautiful caves in the world. Phong Nha Cave has very long underground river (13,969 m) with sandy beaches, contains valuable archaeological artifacts of Champa culture including beautiful ceramic vases. Son Doong Cave contains 4.5 km long passage with maximum height 200 meters and width – 150 meters, here are located also unique cave pearls as large as grapefruits, as well as green, algae covered gours.
- Puerto Princesa Subterranean River – Palawan, Philippines. More than 24 km long cave system with 8.4 kilometers long underground river, which is accessible directly from the sea and navigable up to 4.2 km deep.
- San Wang Dong Cave – China, Chongqing Municipality. 67 825 m long cave with some of the most impressive cave passages and rooms in the world. Cloud Ladder House is the seventh largest cave room in the world, it has its own clouds.
- Shanidar Cave – Erbil, Iraq. Cave has provided important discoveries regarding Neanderthals, such as the information about their funeral ceremonies, care for injured individuals. One Neanderthal found in cave seems to be killed by a human.
- Zhoukoudian – Beijing, China. Famous due to archaeological findings such as one of the first known specimens of another human species – Homo erectus, called also Peking Man, who lived here approximately 200,000 – 750,000 years ago. Cave inhabited also by modern humans in Upper Paleolithic. Remains of numerous extinct animals such as gigantic hyena Pachycrocuta brevirostris.
- Xiaozhai tiankeng – Chongqing, China. Largest sinkhole (tiankeng) in the world, up to 662 meters deep, 625×535 meters across.
- Apollo 11 Cave – Karas, Namibia. Contains some of the oldest cave art in Africa which was created 25,500 – 23,500 BC.
- Blombos Cave – Western Cape, South Africa. Contains the oldest known artwork in the world – at least 70,000 years old engraved pieces of ochre, also 75,000 years old beads of shell.
- Chinhoyi Caves – Mashonaland West, Zimbabwe. Group of legendary, impressive caves with up to 110 meters deep lakes. Extremely high transparency of water where clouds and birds flying over can be seen from 30 meters depth inside the cave lake.
- Kitum Cave and other caves of Mt. Elgon – Trans Nzoia District, Kenya. Unique caves in pyroclastic rocks, up to 250 meters long. Possibly created by elephants and other animals digging the salt in caves up to this day. Kitum cave became known worldwide after two people caught the extremely dangerous and deadly Marburg virus disease in this cave.
- Laas Gaal – Togdheer Region, Somalia. System of caves and shelters with beautiful cave paintings, created 11 – 5 thousand years ago. In this region reported numerous other caves with paintings.
- Sibudu Cave – KwaZulu-Natal, South Africa. Very important Middle Stone Age site. Found the oldest known bone arrow and needle (both 61,000 years old) and traces of heat treated gluing of stone and wood (72,000 years ago).
- Sterkfontein – Gauteng, South Africa. The richest site for early hominins in the world. Found remnants of some 500 hominins, mainly Australopithecus africanus.
- Cave of Swimmers – New Valley, Egypt. Contains some 10,000 years old cave art showing swimming people. Since its discovery serves as a proof for existence of climate changes.
- Actun Tunichil Muknal – Cayo District, Belize. Important Mayan archaeological site with remains of a teenage girl. Her bones by natural processes have been covered with sparkling calcite crystals.
- Bermuda’s Caves, e.g. Crystal Cave – Bermuda. Biodiversity hotspot: in more than 150 caves of Bermudas there are more than 60 species of underwater animals, most of them endemic, representing an eclectic mix of descendants from European, Atlantic, Pacific and deep sea animals.
- Black Hole of Andros – South Andros, Bahamas. Round lake – sinkhole with a layer of violet jelly layer of bacteria at 18 meters depth. Due to this the upper layer of water in this sinkhole is heated up to 40 degrees C°.
- Cave of the Crystals, Naica – Chihuahua, Mexico. Cave with giant selenite crystals up to 12 meters long and 55 tons heavy. Air temperature in the cave is up to 58 °C high.
- El Zacatón sinkhole – Tamaulipas, Mexico. World’s deepest water-filled sinkhole, 339 metres deep sinkhole with 319 meters deep lake. Floating islands in the lake.
- Great Blue Hole – Belize District, Belize. Perfectly round undersea sinkhole, 300 metres across and 125 meters deep.
- Jewel Cave – South Dakota, United States. The third longest cave in the world, total length: 318.6 km.
- Juxtlahuaca and Oxtotitlán – Guerrero, Mexico. Two caves with unique ancient Olmec paintings made 900 – 500 BC.
- Lechuguilla Cave – New Mexico, United States. 222.6 kilometers long cave, one of the most decorated and beautiful caves in the world with unique kinds of speleothems, such as: hydromagnesite ballons, U-loops, up to 6,1 meters long gypsum hairs.
- Loltun Cave – Yucatán, Mexico. Cave with some of the best Mayan cave paintings as well more ancient carvings and remnants of prehistoric animals hunted by Paleoindians.
- Mammoth Cave System – Kentucky, United States. The longest cave system in the world (651.8 km).
- Naj Tunich – Peten, Guatemala. Unusual Mayan archaeological monument in a cave, extremely rich with artifacts. Buildings inside the cave, the only known masonry tombs of elite inside a cave known to science, petroglyphs, inscriptions.
- Pomier Caves – San Cristóbal, Dominican Republic. Series of 55 caves containing the largest collection of ancient rock art in Caribbean, created 2,000 years ago by Taíno, Carib, Igneri people. Approximately 6,000 charcoal drawings and etchings.
- Poza Seca – Tamaulipas, Mexico. One of the unique travertine capped sinkholes in Sistema Zacatón: formerly open sinkhole has sealed itself with a limestone lid. Most likely it hides unknown life forms, not investigated.
- Sacred Cenote – Quintana Roo, Mexico. Human sacrifice site of the ancient Mayan Chichen Itza city. In deposits discovered huge amounts of gold and jade artefacts as well as human remains.
- Sótano de las Golondrinas (Cave of Swallows) – San Luis Potosí, Mexico. The largest cave shaft in the world – enormous 49 x 62 meters wide hole, 372 meters deep. Famous due to a group of green parrots who have to fly ascending in circles around the cave until they get out of it.
- Systema Ox Bel Ha – Quintana Roo, Mexico. One of the world’s largest known underwater cave systems, total explored length – 270.1 km.
- Systema Sac Actun – Quintana Roo, Mexico. World’s largest known underwater cave system next to Systema Ox Bel Ha, total explored length – 346.7 km.
- Abismo Guy Collet – Amazonas, Brasil. The deepest cave in South America and deepest quartzite cave in the world, 671 meters deep.
- Cueva Fell and Pali Aike – Magallanes and Antártica Chilena, Chile. Lava tube where roughly at 12,000 – 8,000 BC lived ancient Patagonians. Remnants of ancient giant Patagonian fauna.
- Cueva de las Manos – Santa Cruz, Argentina. Famous due to paintings of hands on its walls made some 9,000 years ago, often stenciled. Numerous other drawings as well.
- Serra do Ramalho – Bahia, Brasil. Group of large caves with high cave biodiversity, containing endemic species of animals, including endemic fish.
- Sima Aonda – Bolivar, Venezuela. 383 meters deep, ancient quartzite sinkhole, with waterfall and stream flowing through it.
- Sima Humboldt and Sima Martel – Bolivar, Venezuela. 314 and 248 meters deep, ancient quartzite sinkholes located on the top of forested table-top mountains and containing patches of isolated, primeval rainforest on their bottoms.
- Sistema Roraima Sur – Bolivar, Venezuela. Longest known cave system in quartzite, contains numerous unique geological formations. Investigated up to 16,400 meters length.
- Tambolic caves – Amazonas, Peru. Caves with more than 10,000 cave paintings more than 6,000 years old.
- Toquepala Caves – Moquegua or Tacna, Peru. Cave with expressive group of some 7,650 years old paintings.
Australia and Oceania
- Kazumura Cave – Hawaii, United States. The longest lava tube in world, 65.5 km.
- Koonalda Cave – South Australia, Australia. 20,000 years old cave art covering thousands of square meters.
- Minyé sinkhole and cave – East New Britain Province. One of the largest and most impressive tiankengs (giant sinkholes) in world, located in exotic jungle and crossed by powerful underground river. Up to 510 meters deep, 350 meters across, volume – 26 million m³. It continues as a cave system. Explored length of cave passages is 5,421 m, maximum depth – 468 m. Contains one of the largest cave rooms in the world – Tuké room, 240 m long, 200 m wide and 130 m high.
- Nanumanga Fire Caves – Nanumanga, Tuvalu. Undersea caves, approximately 37 – 46 metres under the sea level. Caves show signs of fire left by prehistoric people. This find contradicts with the current assumptions of the sea level changes.
- Waitomo Glowworm Cave – Waikato, New Zealand. The best known glowworm cave, adjusted for the needs of tourism. In many places in this cave (as in most New Zealand caves) walls are covered with larvae of glowworms (Arachnocampa luminosa) emitting blue-green light.
Every year there are reported exciting discoveries of new caves and discoveries of new qualities such as cave paintings in the ones known before. But there still is a feeling that our knowledge covers just a small part of all these monuments of nature.
Though, those which we know offer a surprising diversity of unusual features and impressive sights.
Cave is natural underground space which is large enough for human to enter.
As a separate subcategory there are included also sinkholes – large natural depressions or holes, which for most part represent collapsed caves.
Category includes caves with outstanding characteristics such as large size, significant geological, biological or archaeological values.
Fairly solid rock is required to have rigid cave walls and ceiling. Several geologic processes can create large hollows in such solid rock. Most common ones are:
- Dissolution – hollows are created by the flow of water (in most cases) or gases. Process of the solution is facilitated by the naturally occurring acids in groundwater. This is the most frequent cave formation process which for the most part takes place in limestone, dolomite, marble, gypsum and other comparatively easily soluble rocks. Dissolved minerals in hollows form diverse interesting speleothems – stalactites, stalagmites, columns and also beautiful crystals. Countless caves have beautiful stalactite and stalagmite formations and many show caves are marketed as being the most beautiful ones. Wondermondo will not judge which is the most beautiful one but few will object that Lechuguilla Cave (New Mexico, United States), Phong Nha cave (North Central Coast, Vietnam) or Kap Kutan cave (Lebap, Turkmenistan) are gorgeous. If there is enough time, water can dissolve even quartzite – material considered to be insoluble. The longest known quartzite cave is the 16 kilometres long System Roraima Sur (Bolivar, Venezuela).
- Volcanic proccesses form several kinds of so-called primary caves – caves which form together with the surrounding rock. Lava tubes are created in conditions where hot lava stream gets a harder crust which remains after the lava flows away. Sounds impossible but such process have created even such cave as Kazumura Cave (Hawaii, United States) which is 65.5 kilometers long!
- Erosion processes of the sea waves and streams, but sometimes even wind, often create short caves. Sea caves often have beautiful lighting – only blue rays of the sunlight remain after going through the layer of seawater (Blue Grotto in Capri, Italy).
Many caves are formed otherwise – by glacial processes, earthquakes, biological processes – even by elephants (Kitum Cave in Kenya).
Caves can be unique in several ways: most often due to their geological, biological and archaeological values.
Many caves are adorned with diverse speleothems – specific rock and mineral formations seen only in caves and created by mineral solutions sedimenting the dissolved minerals in cave. Diversity of speleothems is very high and from time to time there are discovered new fantastic forms. Most common speleothems are stalactites, stalagmites, columns and flowstones. Sometimes such speleothems can reach incredible size: the tallest stalagmites can reach 70 metre height (Zhijin Cave in Guizhou, China).
There are also very exotic and rare speleothems such as:
- Cave pearls – limestone balls up to 15 centimetres in diameter. The floor of Gruta de las Canicas (Tabasco, Mexico) is covered with some 200,000,000 cave pearls! Cave pearls are beautiful – sparkling white or with a marble texture.
- Cave ballons – real ballons from minerals! Ballon is made of hydromagnesite and moonmilk (fine, white pasta of carbonate material) and filled with gas.
- Cave showerheads – hollow cones attached to the ceiling of the cave with the narrow end. As if to justify its name one such showerhead in Deer Cave (Sarawak, Malaysia) is the source of shower – waterfall.
- "Champignons" – opal formations of microbial origin in quartzite caves (Venezuela). These weird formations are up to 1 metre across. Quartzite caves in tepuis of Venezuela are known to have several kinds of otherworldly formations, weird symbiosis of minerals and microorganisms.
Cave environment is very beneficial for the formation of crystals. The largest crystals ever found are up to 12 metres long and 55 tons heavy, beautiful translucent crystals of gypsum in the Cave of the Crystals (Chihuahua, Mexico). Often crystals in caves form very beautiful and unusual formations such as white, intricate "trees" of aragonite crystals or gypsum flowers.
Caves have lots of other interesting geological characteristics such as unique minerals, for example sveite is found in Autana Cave (Venezuela), archerite is found only in caves where are bat guano deposits.
The specific cave environment provides shelter for certain species adjusted for more or less permanent life in cave. Scientists have specific names for several groups of cave dwellers:
- Trogloxenes use caves but they need to leave caves periodically to survive, e.g. to get food. Typical trogloxenes are bats. Bracken Bat Cave (Texas, United States) with some 20 million bats is considered to have the largest bat colony of the world.
- Troglophiles are attracted by the caves due to cave environment, but survive in other conditions as well. Famous troglophile is New Zealand glow-worm (Arachnocampa luminosa). Larvae of this small insect attach at the ceiling and walls of many caves and emit blue-green light. This creates unforgettable sights in such caves as Waitomo Glowworm Cave (Waikato, New Zealand).
- Troglobites – animals living only in caves and fully dependant on cave environment. This is very specific group of animals well adapted to a life in total darkness, limited food supply and narrow space. If animal is living in cave waterbodies, he could be called also stygobite.
Troglobites are unique organisms adapted to specific life conditions and high isolation. Cave dwellers can be slow and live very long lives – up to 175 years, they often do not have eyes but other senses are heightened. Hundreds of species of troglobites are found only in one cave and not anywhere else. So far there are known approximately 7,700 species of troglobites but further investigations could increase this number several times.
The largest known troglobite is Black Proteus (Proteus anguinus parkelj) living in few caves of Slovenia. It is up to 35 centimetres long.
The highest cave biological diversity is observed not in tropical regions but in Europe. Most biodiverse is Sistema Postjna-Planina (Notranjsko-kraška, Slovenia) with 84 species of cave dwellers. Unique monument of nature is Movile Cave (Constanţa County, Romania) with 33 species of animals found only in this cave.
Microorganisms in some caves and also sinkholes create unique conditions. Thus the highly unusual Black Hole of Andros (South Andros, Bahamas) is a water filled sinkhole where at the depth of 18 meters is a dark purple layer of toxic sulphur bacteria. In this layer of bacteria due to biochemical processes the water temperature increases up to 36°C. In Venezuelan quartzite caves microorganisms create unusual opal formations – dendrites, "Champignons" and also unusual stalactites.
During the ice age several species of large animals in Europe and Americas found that caves provide suitable habitat in harsh climatic conditions. Developed such species and subspecies of large animals as cave bear (Ursus spelaeus), cave hyena (Crocuta crocuta spelaea), Balearic cave goat (Myotragus balearicus). Evidence of these and many other extinct animals is found in many caves around the world, notably Peştera Urşilor (Bihor County, Romania) with remains of some 140 cave bears.
The history of the development of human has been well preserved in the caves of the world. Sterkfontein Caves (Gauteng, South Africa) contain remains of some 500 early hominins up to 3.3 million years old. Caves contain remnants of extinct human species such as Neanderthals (Homo neanderthalensis) whose last refuge seems to be the southern Iberian peninsula. Here in Gorham’s cave (Gibraltar) have been found the most recent known, around 30,000 – 24,500 years old remnants of Neanderthals.
Most recent another species of human have been found in Liang Bua cave (Flores, Indonesia). This man, Homo floresiensis, went extinct some 12,000 years ago, although there is possibility that these small people lived up to recent times.
Caves contain valuable artwork of prehistoric man such as the oldest known artwork – 70,000 years old engraved pieces of ochre (Blombos cave in Western Cape, South Africa) and the oldest sculpture in the world – 35 – 40 thousand years old "Venus of Hohle Fels" (Hohle Fels in Baden-Württemberg, Germany). Petroglyphs of Bhimbetka Caves (Madhya Pradesh, India) might be even 290 – 700 thousand years old.
Conditions in caves are beneficial for preserving artwork and there are known many hundreds of caves with prehistoric paintings in the whole world. Many cave paintings show that tens of thousands years ago inspiration and skills of artists did not differ too much from that of contemporary artists.
The oldest known cave art comes from Fumane Cave (Veneto, Italy) where barely discernible drawings on the pieces of rocks are some 32,000 – 36,500 years old. Chauvet Cave (Ardèche, France) has 30,000 – 33,000 years old drawings and here the quality of artwork is already very high. Some of the best monuments of cave art in the world are in Cave of Altamira (Cantabria, Spain) and Lascaux (Dordogne, France). Unusual and well matured artistic style is represented in Laas Gaal (Togdheer Region, Somalia). Great 9,000 years old stencil art is represented in Cueva de los Manos (Santa Cruz, Argentina), even more impressive stencils were made by ancient Aborigenes in Cathedral Cave (Queensland, Australia). Unusual are the 6,000 – 8,000 years old pictograms in Edakkal Caves (Kerala, India).
Numerous important archaeological finds have been made in Central American caves. Sometimes around 1,200 – 900 BC have been made Olmec influenced paintings in Juxtlahuaca (Guerrero, Mexico). Maya culture has left important artefacts in sacred wells (cenotes) such as the Sacred Cenote (Quintana Roo, Mexico). Naj Tunich (Peten, Guatemala) – former Mayan ceremonial cave – contains diverse important artefacts: petroglyphs, paintings, ceramics, burials.
Hidden and fragile
Caves in a way are "hidden monuments" because nearly any cave contains very fragile values which are easily lost through unorganised tourism and vandalism.
We can be sure that in every single country, where are found caves, local speleologists (cave explorers) know a huge lot more than is written in tourist guidebooks. But we should not complain about this: unfortunately there is no other way to preserve cave art, fragile crystals and unique, delicate animals living in caves. It feels much better to know that they exist somewhere than to experience a loss of values due to the faulty nature of human.
Caves are found on every continent. The United States is home to the world’s longest cave system, the Mammoth Cave in Kentucky, and to the world’s most popular tourist cave, New Mexico’s Carlsbad Caverns. Great Caves of the World takes readers to these and 25 other astonishing and challenging caves across the globe.
Atlas of the Great Caves of the World is an almanac, encyclopedia, and book of records all under one cover. It is an invaluable reference book for cave explorers and cave enthusiasts of all levels.