It is quite a spiritual experience even for those who don't consider themselves religious.
I've been to Istanbul many times and have experienced the Call to Prayer at all hours of the day and night. It's a great early morning wake up call!
This video is from a visit a few years ago. I recorded it near the Blue Mosque and added images and video -- including some Sufu dancing that I recorded at the old train station in Sultanahmet -- my favorite part of the city.
In my recording, the Call to Prayer starts at the Blue Mosque, but throughout the recording -- you will begin to hear the Call to Prayer start at other mosques around the city. It is quite enchanting to experience it live.