Hagia Sophia went through many designations during its long history of 15 centuries - started as a Byzantine Orthodox Church then as a Catholic Church from 1204 to 1261 and again an Orthodox Church until 1453 when Ottomans conquered Constantinople and converted it to a Mosque. Upon the creation of Turkish Republic, it was designated as a Museum in 1935 until was converted to Mosque again in 2020. It is open to all visitors.