Wikipedia
Sidirokastro (; Bulgarian and Macedonian Slavic: Valovišta; ) is a town and a former municipality in the Serres regional unit, Greece. Since the 2011 local government reform it is part of the municipality Sintiki, of which it is the seat and a municipal unit. It is built near the fertile valley of the river Strymonas, on the bank of the Krousovitis River. Sidirokastro is situated on the European route E79 and the main road from northern Greece ( Thessaloniki) to Bulgaria. It has interesting sights, such as the medieval stone castle, Byzantine ruins, natural spas and beautiful nature.
Sidirokastro ( literally "the iron castle") was a castle in Achaea, Greece, situated between the villages Krini and Kallithea. It is located on one of the foothills of the Panachaiko, the Omplos, near the Omblos Monastery in Zoitada. Little remains of the castle. It is unknown when exactly it was built, most likely by the Franks of the Principality of Achaea. It was used for the defense of Patras, around which the Venetians had built many small castle-fortresses.
It was first mentioned in a list of castles of Achaea in 1364. Nothing is known about its history, although it was situated in a strategical location next to the old road to Kalavryta, known as the Makelarias Road. It is believed that the iron gate of the Omplos Monastery is originally from the castle. The name "Sidirokastro" comes from the slate stones in the vicinity, that are called "sideropetra" ("iron stones") by the locals.