Hagia Sophia

A 4th Century seat of Eastern Orthodoxy and considered the epitome of Byzantine architecture, this beautiful structure became a mosque in 1453, after the Ottoman Empire conquered Constantinople, modern day Istanbul. Inside are mosaics from the early Christian eras from 4th-15th Century as well as remnants of Islam. Now the building is a museum for the past 80 years, with a current exhibit on master calligraphers.