1650 years old. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture. It was the largest cathedral in the world for nearly a thousand years. It served as the cathedral of Constantinople. In 1453, Constantinople was conquered by the Ottoman Turks and Sultan Mehmed II ordered the building to be converted into a mosque. It remained a mosque until 1935 when the newish independent Turkish state secularized it and turned it into a museum.
After visiting Hagia Sophia, we made one more stop. Very cool. The Basilica Cistern. A huge underground water storage vault. Two of the columns had Medusa heads on the bottom which were discovered during renovations.