Dolmuş are shared minivans that run fixed routes all over Istanbul. They cost about the same as buses (15-25 TRY depending on distance) but you get a more local experience and they go places the metro doesn't reach.

Look for the blue and yellow vans with route destinations written on the front windshield. You wave them down like a taxi, pay the driver directly, and hop out anywhere along the route. Great for getting to neighborhoods like Ortaköy or Bebek that are harder to reach by metro. Drivers know every shortcut in the city.