As the sun slid behind the smooth black edge of the world’s most famous caldera, the crowds congregating beside Oia’s hilltop castle erupted in loud cheers, accompanied by dazzling flashes from a thousand cameras. It was like the red carpet at Cannes, but this was an average evening in Santorini, the long-suffering Cyclades island of 15,000 souls that attracts around two million visitors each year.