Looking out over the tranquil expanse of cobalt water that fills Santorini's caldera, it's easy to forget that what you're really seeing is the result of one of the most violent volcanic eruptions in history.

Now a small circular archipelago of islands known as the "Jewel of the Aegean," Santorini was a volcanic cone that erupted 3,600 years ago, causing the landmass to sink and fill with water. What remains is a ring of islands that surround the caldera, forming one of the most striking panoramas in the world.

The largest of the remaining islands is also called Santorini (a.k.a. Thira) and borders the caldera to the east. Its picturesque whitewashed towns, which are perched atop dramatic vertical cliffs, stunning caldera views and unforgettable sunsets, make Santorini the most popular Greek Isle among travelers.

Bordering the caldera to the west is the island of Thirasia, which has a population of approximately 300 people. Just south of that is the small, unpopulated island of Aspronisi. The uninhabited volcanic islands of Nea Kameni and Palea Kameni are located in the caldera's center.