Santorini caldera is a large, mostly submerged caldera, located in the southern Aegean Sea. Visible above water is the circular Santorini island group, consisting of Santorini (aka Thera), the main island, Therasia and Aspronisi at the periphery, and the Kameni islands at the center.

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.

The extraordinary beauty of Santorini's high walls, draped by whitewashed villages, combined with a sunny climate and perfect observation conditions, have made it a magnet for volcanologists and a highlight of tourism in the Aegean.