The natural show of Frasassi Caves with sharp stalactites and stalagmites, Genga, Province of Ancona, Marche, Italy, Europe

The natural show of Frasassi Caves with sharp stalactites and stalagmites, Genga, Province of Ancona, Marche, Italy, Europe

Velika Dolina (Big Valley), a town above the Skocjan Caves, in the Karst Region (Kras Region) of Slovenia, Europe

Castellana caves (Castellana Grotte), Apulia, Italy, Europe

Velika Dolina (Big Valley), a town above the Skocjan Caves, in the Karst Region (Kras Region) of Slovenia, Europe

Castellana caves (Castellana Grotte), Apulia, Italy, Europe

A variety of speleothems including stalactites, stalagmites, columns, straws and drapery at Ngilgi Cave, a limestone Karst cave system near Yallingup in the South West, Augusta-Margaret River Shire, Western Australia, Australia, Pacific

'Bacon strip' curtain formations at King Solomon's Cave in the Mole Creek Karst National Park, the north, Tasmania, Australia, Pacific

'Bacon strip' curtain formations at King Solomon's Cave in the Mole Creek Karst National Park, the north, Tasmania, Australia, Pacific

Natural rock archway carved by the sea through karst limestone rock at Cuevas del mar (sea caves) beach, near Llanes, Asturias, Spain.

Tourist walking on a concrete walkway inside the famous postojna cave in slovenia, admiring the stalactites and stalagmites during a guided tour

Tourists walking on a footpath and exploring the magnificent postojna cave in slovenia, a popular tourist attraction

Tourists walking on illuminated footpath inside the famous postojna cave, a karst cave system near postojna, slovenia

The "Christmas Tree Room" of Florida Caverns State Park, Marianna, Panhandle, Florida, USA

Riesenburg cave, natural karst cave ruin of Frankendolomite, geotope, natural monument, in the back climber at rock face, near Engelhardsberg, district of Markt Wiesenttal, Upper Franconia, Franconian Switzerland, Franconia, Bavaria, Germany, Europe

Versturzhoehle Riesenburg, natural karst cave ruin of Frankendolomite, geotope, natural monument, near Engelhardsberg, district of Markt Wiesenttal, Upper Franconia, Franconian Switzerland, Franconia, Bavaria, Germany, Europe

Chang Cave, stalactite or limestone cave in karst rock formations, Vang Vieng, Vientiane, Laos, Indochina, Asia

Entrance Quackenschloss, passage cave, karst cave, geotope, natural monument, near Engelhardsberg, district of Markt Wiesenttal, Upper Franconia, Franconian Switzerland, Franconia, Bavaria, Germany, Europe

Egyptian temple of Debod, 2nd century BC, at dusk, Madrid, Spain, Europe

The "Wedding Room" of Florida Caverns State Park, Marianna, Panhandle, Florida, USA

Karst cave on the sandy beach near the campsite of Stara Baska, Stara Baska, Island of Krk, Kvarner Gulf Bay, Primorje-Gorski kotar, Croatia, Europe

Limestone Caves at Florida Caverns State Park, Marianna, Panhandle, Florida, USA

Quackenschloss, passage cave, karst cave, geotope, natural monument, near Engelhardsberg, district of Markt Wiesenttal, Upper Franconia, Franconian Switzerland, Franconia, Bavaria, Germany, Europe

Sung Sot Cave, Ha Long Bay, Quang Ninh, Vietnam

Tek (Trimix) speleologist diver in a karstic underwater cave over 70 meters deep, Photogrammetry, twiglight zone, Mayotte

Cave diver in a karst underwater cave at a depth of 60 metres for the Gumbo La Baharini 2 expedition, Passe Bateau Sud at a depth of 60 metres, Mayotte