The castle of the Knights together with the other castles in the area, was built by the Knights of St. John(Agios Ioannis) when Halki, Rhodes and the surrounding islands were under their control. The knights chose the castle's location, where the acropolis of the island used to be in ancient times.

Today the castle blends with the impressive landscape, perched on the rock. Of the remaining buildings you can now see the semi-collapsed walls and the ruins of the church of Agios Nikolaos. Right next to the gate notice the built-in coat of arms of the Grand Master of the Knights Hospitallers, Pierre d 'Aubusson. It is a must to climb up to the castle of the Knights as, besides its archaeological value, it has a spectacular view that will take your breath away.