The inner side of the islands' crescent or CALDERA is predominantly sheer. Overlooking the caldera is where, ideally, you'll want to find accommodations in order to enjoy this unique view called a "caldera view". In my opinion, a caldera view is essential to fully appreciate the majesty of Santorini and the good news is there are many price ranges to select from: luxurious to budget. Quantities are limited however.
The film The Sisterhood of the Traveling Pants was filmed partly on Santorini, offering some stunning views of the island. You may recall the scene where one of the girls wanted to show off her photos the caldera, but the other girls were only interested in photos of the handsome Greek man.
Back from the cliff's edge, the land gently slopes to the sea broken by the Hills of Profitis Illias (565m /1,875 ft.), St. Illias (1,105 ft.), Inner Vouno (1,100 ft.) and in the north Big Mountain (1,092 ft.). Vouno means mountain in Greek.
Santorini's central islands are called the Kameni or 'burned' and are the result of lava flow. The whole island group is one big volcano made of marble and metamorphic schist. The lagoon, formed by the volcanoes implosion, is 380 meters or 1,216 feet deep. It's 10 km wide. By comparison, in 1889, Krakatoa's crater was only 3 km and sent clouds of ash around the world.
Throughout its turbulent history the island has changed shape as a result of eruptions. Of the smaller islands, only Aspro ('white' in Greek), to the SW, is of the original land surface. In 236 BC additional activity severed Thirassia from Thiras' NW corner. In 196 BC Hiera or Old (palia) Kameni rose from the sea. In 146 BC the islet of Thia came into view and then sank. The south coast of Thira sank taking with it the port of Eleusis in 1570. After three years Small Kameni arose and in 1711 New Kameni. In 1866 major erupting commenced and lasted for 2 years producing the George I Volcano on Big Kameni and the islet of Aphtoessa which then sank in 1868. Mikro and Nea Kameni were joined by further erupting in 1925. An earthquake caused major damage to Thira, the big island, in 1956, destroying one-half or more of the buildings on its west coast. Today, geologically speaking, things are quiet and safe for all.