Above the old abandoned village Horio stands the Castle of the Knights on the hill of Agios Nikolaos in Halki. The castle was built form the Knights of St. John during the 14th century while it was surrended to the Ottomans in 1522. You can reach this castle through an uphill path that starts from the church Panagia leading to Horio. At the entrance of the castle you will see a built-in cioat of arms of the Master of the Knights with the church of Agios Nikolaos.