As a result of the country’s rich geological structure and evolution, thousands of magnificent subterranean and underwater caves were formed both on the mainland and on the islands. Systematic explorations conducted by geologists and speleologists have brought to light more than 8,500 caves of all categories (caves, abysses, underground rivers, etc), many of which still remain unexplored.

Caves were gradually formed on Greek land during the Tertiary and Quaternary Periods, while their large number is due to the huge quantities of limestone covering about 65% of the country’s surface. Many of these caves have given vessels, bones, rock paintings, jewelry and traces of fire, as well as a host of other findings attesting to a very early human presence. Many of these caves were used in antiquity as sites of worship, while in later times they housed churches and monasteries; many caverns situated on steep slopes were used by monks as hermitages. Moreover, numerous caves have played an important role in Greece’s struggles for independence (since they served as shelters, hideaways, hospitals, workshops, etc.).