Entrance of the Orecchio di Dionisio cavern, Neapolis, Siracusa, Sicily, Italy, Europe

Interior of the Orecchio di Dionisio cavern, Neapolis, Siracusa, Sicily, Italy, Europe

Drone view of Matala artificial caves on the rock by the beach at Crete, Greek Islands, Greece, Europe

Woman and man relaxing in salt cave

Venus Grotto of King Ludwig II, artificial stalactite cave with a lake and a shell-shaped boat, painting "Tannhäuser bei Frau Venus" by August von Heckel, palace gardens of Linderhof Palace, Upper Bavaria, Bavaria, Germany, Europe

Artificial ice cave, Perlan, Reykjavik, Hoefuoborgarsvaeoio, Iceland, Europe