The Haghia Sophia (Aya Sofya) is a church dating back to 1228-1263. It houses some very fine frescoes. It is a major sight of the city.

Here you look up into the cupola. It's a new edit of a slide I scanned again and edited in 2018.
I was informed the saint to the left is St Symeon Stylites the Elder in praying (orans) position. The one to the right is St Symeon Stylites the Younger holding a cross.