While you are seeing the latter - which in a way is a modern mall less chain stores - see also the Cystern (an underground water tank from the Roman times http://www.sights-and-culture.com/Turkey/Justinians-Cistern.html
the Hagia Sophia (or Aya Sofia as the local say it) http://www.greatbuildings.com/buildings/Hagia_Sophia.html
and the Blue Mosque http://www.guideistanbul.net/sultanahmet.htm
The Topkapi palace http://www.guideistanbul.net/topkapi.htm especially the Harem part is another must-see.
Wojtek