Time Out says
Perhaps the most cherished green space in Istanbul, the Belgrad Forest is a wooded wonderland spread out across more than 1300 acres. A popular weekend destination, the forest has designated picnic areas and a 6.5 km track used by joggers and walkers. It begins at the Neşet Suyu fountain and has markers every half kilometer so you can track your distance. Once you've taken a few steps into the forest you'll quickly feel the revitalizing touch of the fresh, clean air.