On the record: one on The 50 Best Bars.

Bar Gabriel calls itself a neighbourhood bar for cocktails and small bites, first come first served, with no reservations.
Çırağan Bar sits on the entrance floor of Çırağan Palace Kempinski, the palace hotel on the Bosphorus. It offers a refined setting with a collection of premium spirits, signature cocktails and gourmet snacks, built around pre dinner aperitifs to live music. Reservations are not taken, and the dress code is chic casual.
Mikla Bar is the roof terrace bar at the top of The Marmara Pera, run alongside the Mikla restaurant. The setting is chic and minimal, with an outdoor pool, a DJ playing mellow music and views over Galata and the old city as the sun sets. Martinis and signature cocktails lead the drinks, backed by a wine list focused on Turkish producers.
These bars are the starting point. The full BarMagazine directory covers every listed bar in Istanbul, with a map, filters by bar type, and new openings as we verify them.