The island of Santorini is unique for many reasons, and arguably all of them derive in some way from the formation of the caldera; the bowl-like crater that was formed when the land cracked and sunk into the sea after the volcanic eruption over 3,500 years ago. The caldera cliffs that ring the volcano we see today in the middle of the lagoon, rise up to 400 metres in places. The cliffside villages of Oia, Imerovigli, Firostefani and Fira cling to the sides of the cliffs.