Atlas Pasajı (passage) is the street fashion center where you'll find "original design" clothing, accessories, bags etc. for reasonable prices. Most famous shop is "Raven", don't miss. There are 44 shops inside and these shops are at the back side of the passage, so don't forget to visit upstairs.
If you're interested in history, visit art gallery inside the passage for architectural details. The history of the building dates back to 1870 which was build as a winter residence by a rich family and restorated in 1932 as a shopping mall.
Atlas passage is on your left, Nr.209. The signboard is really small but you'll notice movie posters at the entrance.