In the center of the upper gallery is where the Empress’ Loge was located. The Byzantine empress would sit on a throne next to the ladies of her court and watch the church services down below. The view is spectacular from there, but it’s even better when there is no scaffolding (only once in all of my visits).
On the southwest corner of the upper gallery is the door to the Patriarch’s office and the other offices of the Ecumenical Patriarchate of Constantinople. It’s closed to the public and it isn’t know what’s behind those doors today besides storage space.
Also on the southwest corner is the beautiful marble door to the meeting chamber of the Holy and Sacred Synod. The Synod is a council made up of the Ecumenical Patriarch and a group of bishops. They have met since the 4th century to make decisions about issues under the jurisdiction of the Patriarch.
Once through the door, other than several Byzantine mosaics there are a few interesting things to spot. Graffiti made by Viking mercenaries can be found on the center of the marble bannister. All of them are illegible except for one that translates to “Halvdan was here”. The graffiti is from the 9th century and is attributed to the Varangian Guard, a regiment of Vikings that fought for and protected the Byzantine Emperor from the 10th to 14th centuries, and as early as the 9th century.
Back towards the windows is a gravestone for Enrico Dandolo. Dandolo was the Doge of Venice and commanded the Fourth Crusade. Blind and 97 years old at the time, he was responsible for the Sack of Constantinople and looting Hagia Sophia in 1204. The Byzantine Empire went into exile in Nicaea (İznik) and the Latin Empire ruled Constantinople until 1261. Dandolo died in 1205 and was buried in the church, but his tomb was later destroyed by the Ottomans. The gravestone is believed to be near the actual tomb.
Looking out the windows on the south side of the upper gallery, it’s possible to get a good view of Sultan Ahmet Camii (Blue Mosque). The mosque was built to rival the grandeur of Hagia Sophia.