St. Sophia Museum;
The ancient basilica, built by Constantine the Great in the 4th century and reconstructed by Justinian in the 6th century, is one of the architectural marvels of all time.
St. Sophia Museum was a Greek Orthodox Christian patriarchal basilica (church), later an imperial mosque, and now a museum (Ayasofya Müzesi) in Istanbul, Turkey. The Roman Empire's first Christian Cathedral, from the date of its construction in 537 AD, and until 1453, it served as an Eastern Orthodox cathedral and seat of the Patriarch of Constantinople, except between 1204 and 1261, when it was converted by the Fourth Crusaders to a Roman Catholic cathedral under the Latin Empire. The building was later converted into an Ottoman mosque from 29 May 1453 until 1931. It was then secularized and opened as a museum on 1 February 1935. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture and is said to have "changed the history of architecture". It remained the world's largest cathedral for nearly a thousand years, until Seville Cathedral was completed in 1520.
With The Following organization of Istanbul Daily Tours, you can visit the St. Sophia Museum.