Agios Ioannis sto Kastri has tiny isolated beaches with beautiful transparent turquoise waters. It is named after Agios Ioannis chapel located on a rock in the sea. Agios Ioannis chapel has become famous all over the world because it the wedding location of "Mamma Mia movie". You will find it on your way to Glossa. The small beaches are opposite the chapel.
You may see the photos of the shootings of Mama Mia in the Agios Ioannis chapel, with Merul Strip, Pierce Bronsnam and the rest of the cast.