For many visitors, sightseeing in Istanbul is as much about shopping as museums and monumental attractions, and the Grand Bazaar is where everyone comes 

This massive covered market is basically the world's first shopping mall; taking up a whole city quarter, surrounded by thick walls, between the Nure Osmanıye Mosque and Beyazıt Mosque 

The Beyazıt Mosque (built in 1498-1505) itself occupies the site of Theodosius I's Forum and has architecture inspired by the Aya Sofya.