Near Taksim Square
We stayed in a hotel near Taksim Square, so I did all my running near there. I started near Taksim Square and then ran south on Istiklal Cd., a mostly pedestrian street, that has the nostalgic tram running down the middle. In the mornings, there are also delivery vans parked on the street but it's still pretty easy to run as the street is reasonably wide. When you run past the ending point for the nostalgic tram (which is also where the Beyoglu funicular starts/finishes), Istiklal Cd. turns into Galid Dede Cd. and starts sloping downhill. When the road starts sloping downhill more steeply, it also changes name (though I never saw road sign) to Yuksek Kaldirim Cd. At the bottom of the road, cross the street and then you can cross the Galata Koprusu (Galata Bridge) into the historical peninsula. The road tracks the Golden Horn (the waterway between the two halves of the European side; the Galata Koprusu crosses the Horn) and there are sidewalks you can run on quite a ways.