From Imerovigli, a sign points west for the track to Skaros, the conical peninsula jutting out into the caldera. Not only geologically interesting, it is also historically important, as it was the first of five kasteli (fortresses) built on Santorini in the 15th century to protect the islanders from pirate attacks. Earthquakes put an end to that, however, and the inhabitants moved to Fira. Walk out for great views and a perfectly situated church, but expect plenty of steps.