Iznik Ayasofya Museum (Hagia Sophia Museum in Nicaea) One of the most important centers both for the Ottoman Empire and Anatolia, the Iznik County houses this museum, converted from a mosque, which was formerly the church where the seventh Ecumenical Council was held.
Originally dating from the Roman period, the building was converted into a mosque in 1331, and today it serves as a museum. The frescoes and mosaics from the Byzantium period, together with the sarcophagi are worth seeing.