Korčula is a Croatian island in the Adriatic Sea, off the mainland's Pelješac peninsula. The town Korčula is known for the medieval towers and walls fortifying its harbor. Its central square features the Cathedral of St. Mark, begun in the 14th century. The island's beaches include Vela Przina, a wide crescent that's popular with families, and Pupnatska Luka, a turquoise cove.