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Photo: Adli Wahid, CC BY-SA 3.0 via Wikimedia Commons
The third and grandest of the churches on this site, completed in 537 AD. The 30-m diameter dome covers what was for over 1000 years the largest enclosed space in the world, only surpassed in 1520 by Seville cathedral. It used "pendentive" architecture to throw the dome's weight onto four stout pillars, a design that inspired many Eastern Orthodox churches and Ottoman mosques. It became a mosque after the Ottoman conquest in 1453, remaining so until 1931. It was then a museum until 2020 when it was again proclaimed a mosque. That means you must work around prayer times and dress appropriately. Very cheap disposable headscarves are available for purchase outside the building.
Hagia Sophia, officially the Hagia Sophia Grand Mosque, is a mosque and a major cultural and historical site in Istanbul, Turkey. It was formerly a church (360–1453) and a museum (1935–2020). The last of three church buildings to be successively erected on the site by the Eastern Roman Empire, it was completed in AD 537, becoming the world's largest interior space and among the first to employ a fully pendentive dome. It is considered the epitome of Byzantine architecture and is said to have "changed the history of architecture". From its dedication in 360 until 1453, Hagia Sophia served as the cathedral of Constantinople in the Byzantine liturgical tradition, except for the period 1204–1261 when the Latin Crusaders installed their own hierarchy. After the fall of Constantinople in 1453, it served as a mosque, having its minarets added soon after. The site became a museum in 1935, and was redesignated as a mosque in 2020.
© OpenStreetMap contributors
Bathhouse built in 1556 by Mimar Sinan, the chief Ottoman architect, at the request of Hürrem Sultan (Roxelana), wife of Suleiman the Magnificent. It was built over the former public baths of Zeuxippus, abandoned around 713. Restored in 2011, it's now an upmarket spa.
Yerebatan Sarnici
Vast underground cistern built by Justinian in 532 to store the city's water, the largest and best-known of the hundreds constructed. It's a cathedral-like space with 336 richly decorated columns. Time was you explored in a little rowing boat, but tourist numbers have soared and water levels have dropped, so now you follow a boardwalk, with lights, piped music and art installations. It's sometimes a film location, and stages concerts. But the crowds rob it of atmosphere and you might prefer to seek out one of the less-visited cisterns.
İstanbul Arkeoloji Müzeleri
Turkey was slow to protect its antiquities and to display them properly, but in 1867 Sultan Abdülaziz toured the museums of Paris, London and Vienna and saw what was needed. The main collection is in a grand neo-classical building of 1891, with two annexes for ancient art and Islamic art. Exhibits include Sumerian tablets, pieces of the wall of Babylon, Roman statues, and the Alexander Sarcophagus. There are very detailed historical explanations in both Turkish and English. There is also quite an accurate exhibition about the historical layers and epochs of the city of Troy. If you are passionate about history, you can spend many hours here, so bring a supply of water and food (the museum café is quite expensive). In the summer, on Saturdays and Sundays, they have concerts in the courtyard.
Built in 1741, the last major hamam opened in the Ottoman era. It has ornate architecture, great service and a stellar cast of famous visitors. Prices to match, and only tourists now use it.
Blue Mosque
The defining image of Istanbul, dominating the skyline with its great dome and six minarets. Completed in 1617 for Sultan Ahmed I, it's still a working mosque, so dress appropriately and avoid prayer times. Enter via the courtyard on the SW side. You step (shoeless) into the blue-tiled prayer hall beneath the main dome and its semi-domes. The mihrab is of finely carved marble, well-lit, and the minbar (pulpit) next to it is visible from almost all parts.
İslam Bilim ve Teknoloji Tarihi Müzesi
Museum in a restored building that was the stables for Topkapı Palace. It exhibits various instruments for astronomy, clocks, pumps, weaponry, a steam-powered döner spit, and so on developed in Islamic realms down the centuries, but these are modern repro, and explanations of their context are skimpy. Islamic science and technology preceded that of Europe, as they insist, but they get the tone wrong, as if that was the triumphal culmination rather than the springboard for further advance.