One of the most glorious things to do in Istanbul is take in the sunset and twilight light on Hagia Sophia. The proper vantage point is between the venerable church (then Mosque, then museum) and the nearly equally famous (but not nearly as impressive or historic) Blue Mosque, from which nice views of the latter can also be had. Patience rewards one with a transition of stunning views—and you can grab a durum döner to go at the adjacent Dervish Cafe and enjoy it with the changing light.
Thanks for looking! 
A.D. 