The Knights Castle, formerly known as Neratzia Castle and built on the ruins of an ancient fortress, stands just at the entrance of the port of the town of Kos. Its construction began in the14th century by St. John's Knights because of the delays caused by Turkish invasions. The castle has two rounds of walls and was an islet until the beginning of 20th century, as in the place of today’s Foinikes Avenue there was a ditch filled with sea water separating the castle from the land.
The castle was connected to the mainland near the location of Hippocrates Plane tree by a bridge which is still preserved on Foinikes Avenue.
In Antimachia, 4.5 km SE of the village there is a very well preserved medieval castle. Ruins of a Byzantine castle are still preserved on top of a hill in Pili offering the visitors an amazing view of the nearby islands, while more castle ruins can also be found on top of the hill in Kefalos.