St. John was built in 1876 at the center of Poseidonia with the donations of George Veltsos, Themistocles Petrokokkinos as well as various precious sacred relics and icons of the 19th century sent by Zanis Petrokokkinos from St. Petersburg.
It is a church of Byzantine style with a dome and cruciform painted in the colors of the Greek blue sea and the azure sky. In the elder years, on August the 29th visitors used to camp around the temple, light up the beach with lights that were placed on the boats and mansions in honor of the Saint.
The celebration continued with live music, dancing and singing and the procession of Saint John with the accompaniment of music, a custom still celebrated to the day.
