We have all seen pictures of the glorious interior spaces of Hagia Sophia. I need not post another. But I will highlight the oldest architectural feature of the cathedral-turned-museum. It was new to me and it has stayed with me as one of the memorable images of my visit.
The Nice Door dates back to 2C BCE. It was once in a pagan temple and brought to the cathedral by Empire Theophilos in 838. In the bronze one reads two things: "God and Christ Help Us", and the year 838 (monogram).