Atmospheric. Literature in all languages of the world. Merchants are sociable, they don't always understand English well, they often understand Russian better) They also sell cards, postcards, coins, pages with beautiful miniatures, wooden stands for the Koran and many other things to read! I recommend you to visit!
Probably a good place for those who read in Turkish) There are practically no books in English. It is easier to find from Istanbul University than from the Grand Bazaar.