The unique attraction of Santorini is its geological character, the sheer walls of striated and multicolored pumice, black lava, slag, ash, and pozzolana, rising up sheerly 305 meters (1000 feet), half encircling the deep blue waters of the caldera created by the explosion of a volcano sometime around 1600 BC.
Atop those sheer cliffs one sees the familiar white Cycladic architecture. The caldera is about 10 km (6.2 miles) in width and 380 meters (1246 feet) deep, with two islets amid its waters, Thirasia, or Palaia Kameni, and Nea Kameni, both volcanically active.
There have been many earthquakes in this extremely seismic area, a serious one in 1956 killing 50 people and destroying 2000 homes, though that doesn't keep anyone away.
The best approach to Thira is by sea, for the full impact of this amazing island, and by a boat smaller than the large ferries, the smaller ports of Skala Firas and below Ia.
There are 593 steps up to Fira from Skala Firas, taking most people about 40 minutes on foot though there are delightful hired mules, and also a cable car (which is rather interesting). Austrian built, it was donated to the island by a Greek ship owner, and profits go to a community fund and to the donkey drivers.
The capital town is called Fira (pronounced Feer-AH) gets packed in high season, a good time to avoid the place if possible. On the road to Ia from Fira there are two youth hostels.
Fira' s architecture is typically Cycladic, with white houses, blue domed churches and chapels, winding streets. The views over the caldera are stunning, the ones from the Orthodox cathedral especially so.
Vineyards slope down to the Aegean behind the town. The newer district to the north, was rebuilt after the 1956 earthquake with curved roofs to withstand tremors. The Roman Catholic community and cathedral in this area stem from the Venetian occupation; a Dominician convent next to it has a carpet weaving workshop, open to visitors, with items on sale. The Museum Megaro Ghizi, housed in an old mansion, has fine collections (ceramics, furniture, engravings, prints and maps, costumes, etc with photos of Fira before the 1956 earthquake. The Archaeological Museum north of town displays sculptures and ceramics from Thira (Mycenaean to Roman times), some Early Cycladic figurines unearthed in the pumice mines, and more. There is also the Folklore Museum in an 1861 cave house with its household items on display. The Thira Foundation has chambers carved into the cliffs that hem the caldera, with beautiful photographic reproductions of the frescoes from Akrotiri (see below). A newer museum on the south end of Fira, has Cycladic art and fossils, and finds from Akrotiri. Firostefani village, to the north of Fira, has merged with it and with Imerovigli to its north. The medieval island capital, sits up over the caldera on a large volcanic rock with a Venetian fortress below it in front of Imerovigli, and in the same town are ruins of a 16th century Catholic convent, and a new church with a beautiful carved wood iconostasis salvaged from the church destroyed in the 1956 earthquake.