The city of Santorini is located in the southern Aegean Sea, about 200 km southeast of Athens. It is the largest island of a small, circular archipelago that is the remnant of a volcanic eruption. The city is perched on the edge of a cliff, overlooking the caldera (a large, sunken crater). The whitewashed houses and churches of the city are a striking contrast to the blue-black lava cliffs. The city is a popular tourist destination, with many visitors arriving by cruise ship.