Unfortunately, Istanbul can be limited in terms of good places for a run, because the streets are windy and usually full of traffic. That said, here are a few ideas for a jog.
Along the Bosphorus. On the European side, from Ortaköy northward along the Bosphorus, is a long, mostly uninterrupted path along the water. Race with the ships that slip by at eye level and gaze over to Asia as you run. Be aware that fishermen and others use the pathway, particularly around Arnavutköy / Bebek / Emirgan, so be prepared to dodge some crowds and some casting lines.
Bostancı. On the Asian side, a long path along the Sea of Marmara gives unparalleled views of the old city peninsula and Prince’s Islands. A bit out of the way, perhaps, but worth a trip for the view. Perhaps combine it with a visit to Kadiköy for a post-workout snack.
Belgrade Forest. A forest? In Istanbul? Yes. North, just up the hill from the Bosphorus communities (see neighborhood guide here), a 21-square-mile swath of preserved land makes up the Belgrade Forest. Trails abound, but the most popular is a beaten 6km route. Get there early on weekends to beat the crowds.
Sultanahmet / Old City. Running in this area is difficult as the streets can be jammed. But, if you’re an early bird, get out while the rest of the city is still sleeping (really anytime before 8:30), and beat your own path around the historical sites, including the oasis of Gülhane Park.
Emirgan Park. If you are hankering for some hills, make your way to Emirgan Park, then up the steep streets and paths around this well-tended green space. Treat yourself to a tea in one of the historical villas inside the grounds (köşks), each known by their color – Pembe (pink) Köşk, Beyaz (white) Köşk, and Sarı (yellow) Köşk.
Inside. Not ideal for seeing the sites, but you might absorb a bit of culture. Check out one of Istanbul’s fitness emporia, where locals go to work out, chill out and socialize. The MAC chain has an outpost on Maçka Park between Nişantaşı and Beşiktaş, convenient to the center of the city, though the Bebeköy branch has a pool with some of the sweetest views in the city.
Also, if you like some competition, don't miss out on these chances to join a running event in Istanbul:
During the Avrasya Maratonu in November you will be crossing the bridge and run from Asia to Europe.