One of the most memorable moments of our trip to Sifnos happened while we were hiking down the valley below Apollonia, and Kastro village suddenly came into view. The centuries-old settlement perched on a cliff high above the sea was one of the most exhilarating and breathtaking sights we have ever seen while walking in Greece. Built between the 14th and 18th Centuries, Kastro was the capital of Sifnos during the medieval period. It’s a must-see if you ever visit the island.