The small church of Agios Nikolaos “Maroulainas” is located to the northeast of Kastania. It is a cross -barrel-vaulted type church, built probably in the second half of the 13th century. It has an orthogonal ground plan, with a semicircular apse at the east and the entrance at the west. Its masonry is rather plain, made of rubble, with limited use of brick fragments in the joints, in horizontal layers, apart from the north wall which is undecorated. The western side is more elaborately arranged; a blind relieving arch over the entrance is bordered with oblique bricks and a dented band. Above that a plate socket is preserved. The interior is decorated with wall paintings, mostly contemporary to the church’s construction. Later additions, probably of the 18th century, are the figures of the built templon (screen or iconostasis) and the re-painted Agios Nikolaos on the north wall.