Santorini is a small, circular group of volcanic islands located in the Aegean Sea, about 200 km south-east from the mainland of Greece. Its spectacular natural beauty along with its eminent nightlife make the island one of Europe's top tourism hotspots.
A giant central lagoon, more or less rectangular and measuring about 12 km by 7 km (8 mi by 4 mi), is surrounded by 300 m (984 ft) high sheer cliffs on three sides. The island slopes downward from the cliffs to the surrounding Mediterranean sea. On the fourth side, the lagoon is separated from the Mediterranean by another much smaller island called Therasia, also with cliffs. The lagoon is joined to the sea in two places, in the northwest and southwest. The water in the centre of the lagoon is nearly 400 m (1,300 ft) deep, so it is an ideal safe harbour for even the biggest ships. The island's ports are all in the lagoon and there are no ports on the outside of the island. The towns of Santorini cling to the top of the cliff looking down on the lagoon.
The island was the site of one of the largest volcanic eruptions of the last several thousand years when it erupted cataclysmically about 3,500 years ago.