One of the most famous attractions of the island is the volcano of Santorini, one of the biggest active underwater volcanoes in the world. Its biggest eruption occurred 3,600 years ago, causing a tsunami so powerful that it obliterated the Minoan civilization of Crete. This eruption also caused a large part of the island (which was then named Stroggyli due to its circular shape) to sink, thus giving shape to the island of Santorini as it is today, as well as the islands of Thirasia and Aspronisi which are located around the caldera.
Some of the most famous towns of the island are built in the caldera, namely Fira, the island's capital, Oia and Imerovigli, but also the island's main port and many volcanic beaches.
From some later volcanic eruptions that took place in the 17th century, two more small islands were formed in the caldera, Palaia Kameni and Nea Kameni.