In many interesting ways caves have been linked with the history of man. Caves are deep hollow places in the rocky sides of hills or cliffs. Large caves are called “caverns.” Today, huge and beautiful caves all over the world are tourist attrac­tions. Caves are formed in many different ways such as by the constant beating of the sea waves against the rocks. Caves that appear under the surface of the earth are usually formed due to the old courses of underground streams that have worn away layers of soft rock such as limestone. While others are formed by the volcanic shifting of the surface rocks or by the eruption of hot lava. Some caves have galleries in tiers or rows, one above another. Underground streams wind through some caves, though in many cases after a cave has been formed, the streams that once flowed through it may find a lower level and leave the cave dry.