A representative example of pre-Byzantine architecture, the church of Agios Apostolos, at the beginning of Olympus Street, is a Byzantine monument of UNESCO world cultural heritage. Built-in the period 1310-1314 by Patriarch Niphon I, it was the catholic a large monastery dedicated to the Virgin Mary. The temple took its name from the twelve domes that represented the twelve Apostles. An architecturally impressive church, with an unusual ratio of height and width, with a type of complex five-domed four-column cruciform inscribed with a narthex and a vestibule with two chapels to the east. Its interior decoration is a masterpiece, with rich and intense mosaics, iconographic sets, and murals of high artistic quality.
The church was converted into a mosque in the early 16th century. From 1926 the gradual restoration of the decoration began and from 2002 the cleaning of the mosaics again highlighted the richness of their colors.