Chrysocherias Castle or Pera castle is a Frankish castle of Kalymnos between Pothia and Chora. It owes its name to the church of Panagia Chrysocheria which is located inside and existed before its construction.
The castle has two towers and two gates and a rampart.
The castle is known for the three windmills that survive today outside its eastern wall.
Traces of habitation from the Neolithic era have been found at the site of the castle. Before the construction of the castle on the site there was an ancient temple whose parts are built into its walls. Above its east gate are the coats of arms of Guerini and other governors of the island.
The castle was built in the 15th century by the knight commander Fantino Guerini by order of the Grand Master of the Knights of St. John of Rhodes Jean de Lastic who wanted to fortify for protection all the islands that belonged to the order. Guerini, because the Great Castle already existed for the defense of the island, wanted to build a castle owned by him with the obligatory work of the inhabitants. The inhabitants reacted and refused, then Guerini referred them to a trial where he was acquitted, so the construction of the castle of Chrysocheria began.
The castle was abandoned very quickly, in the middle of the 15th century, unable to withstand the raids of the Ottoman mainly pirates.