Kastelli is an imposing, seaside Byzantine castle in northwestern Kalymnos, built on the rocky edge of Cape Aspropountari. It is opposite the castle of Agios Konstantinos Telendos and kept in close contact with the Galatiani Castle. On the southeast side of the mountain, which dominates the castle, there is the church of Virgin Mary of Kastelli, which is accessible. The view from the mountain is stunning and will reward you as you can only reach it on foot.
It was built during the Byzantine period to deal mainly with the Arab raids and controlled the sea passage between Kalymnos and Telendos. It had walls, towers for better defense, a walled citadel with access from a staircase, and three gates. Inside, the ruins of numerous buildings testify to the existence of a settlement. The period during which it was abandoned is unknown. However, it is rumored that in the 10th century its use began to decline until it was completely abandoned.
To reach the castle you will need to leave your transport on the main road and then continue on foot.