Santorini also known as Thera is a volcanic island located in the southern Aegean Sea, about 200 km  southeast from Greece's mainland,  member of the Cyclades group of islands, with a population of 14,000.
Santorini is essentially what remains of an enormous volcanic explosion, destroying the earliest settlements on what was formerly a single island, and leading to the creation of the current geological caldera. A giant central lagoon, more or less rectangular, and measuring about 12 by 7 km is surrounded by 300 m  high steep cliffs on three sides.On the fourth side, the lagoon is separated from the sea by another much smaller island called Therasia. The water in the centre of the lagoon is nearly 400 m (1,300 ft) deep, thus making it a safe harbour for all kinds of shipping. The capital, Fira, clings to the top of the cliff looking down on the lagoon.
Santorini  is the most active volcanic centre in the South Aegean Volcanic Arc, though what remains today is chiefly a water-filled caldera. The island is the site of one of the largest volcanic eruptions in recorded history: the Minoan eruption (sometimes called the Thera eruption), which occurred some 3,600 years ago at the height of the Minoan civilization. The eruption may has  led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km (68 mi) to the south, through the creation of a gigantic tsunami.This theory is not, however, supported by chronology, in that the collapse of the Minoan civilization did not occur concurrently with the date of the Tsunami . Another popular theory holds that the Thera eruption is the source of the legend of Atlantis.