Santorini caldera is a large, mostly submerged caldera, located in the southern Aegean Sea, 120 kilometers north of Crete in Greece. Visible above water is the circular Santorini island group, consisting of Santorini (classic Greek Thera), the main island, Therasia and Aspronisi at the periphery, and the Kameni islands at the center. It has been designated a Decade Volcano.

The caldera measures about 12 by 7 km (7.5 by 4.3 mi), with 300 m (980 ft) high steep cliffs on three sides.

There are two small volcanic islands at the center of the caldera, Nea (“New”) Kameni and Palea (“Old”) Kameni.