Cleveland Avenue passage in Mammoth Cave System, Kentucky, United States of America, North America

Interior of the Gruta do Janelao, a limestone cave passage 100m high, lit through roof window, at Peruacu in Minas Gerais state, Brazil, South America

A caver in a tight squeeze in the Yorkshire Dales, England, United Kingdom, Europe

Cavers in County Pot in the Yorkshire Dales, Yorkshire, England, United Kingdom, Europe

Inner court shopping centre Quartier 206 Friedrichstrasse Berlin Germany

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

Rock gate Geisskirche, passage cave, mystical, hamlet Tuerkelstein, district of Goessweinstein, Upper Franconia, Franconia, Bavaria, Germany, Europe

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

Undergroun caves, Camerano, Marche, Italy

A tight squeeze for travelers exploring New Zealand's famous Franz Josef Glacier, iwth its blue Ice, deep crevasses, caves and tunnels that mark the ever changing ice formations; West Coast, New Zealand

Travelers exploring the famous Franz Josef Glacier with its, blue ice caves, deep crevasses and tunnels that mark the ever changing ice formations; West Coast, New Zealand