Chrysocheria Castle or Pera Castle is located between Pothia and Kalymnos Town. It is a Frankish castle and owes its name to the church of Virgin Mary "Chrysoheria" which is inside it and existed before its construction. It was built in the 15th century by the Knight Commander, Fadino Guerini, under the command of the Grand Master of the Saint John Knights of Rhodes Jean de Lustique, who wanted to fortify all the islands that belonged to the Battalion for protection. The castle has two towers, two gates and pre-casting. It is also known for the three windmills that survive to this day, outside its eastern wall.