To the north-east of Chora of Kalymnos, there is the Byzantine castle. It was built in the 11th century AD and it was reconstructed in late15th century. It was the residential centre of the medieval Kalymnos, from where the settlement of Chora began its expansion. In this castle, there are ten churches in which there are wall paintings dating back to the 15th-16th century. In order to reach this place, you have to follow the uphill road that heads to the mountain starting from Pothia. The route can be quite difficult for those who are not used to walking, since the castle is located at the highest point of the mountain.