Fairly straight forward, got a taxi from one of the many taxi desks in the airport,50 Euros for what was a 45 minute trip.
I’m staying in what I believe to be the newer part of Istanbul it’s about 40 minutes to the center of the old town depending on traffic. Depending on the time of day traffic is a problem. I arrived late in the evening so not so much a problem from the airport but traveling to and from work is anything from 20 to 40 minutes for a three mile commute.
Interesting old town though.
Cheers