Kythnos or Oria or Katakefalos Castle
The castle was the medieval capital of the island of Kythnos fron 7th century AD until the end of the 16th century. Those days it was called "Castle of Thermia". Thermia was the name of Kythnos because of the hot springs in the island that were famous since the Roman era.
From 1207 the island and the castle belonged to the Italian family of Gozzadini who were subjects of the Venetian Duchy of Naxos. In 1537 the castle was destroyed by the Turkish pirate Barbarossa. It took some time for the capital to move to Messaria (or Chora). This happened in 1570, while the Venetian era finished in 1613.