Istanbul is a pedestrian's paradise. There is always something interesting to see as one visits its various neighborhoods, explores its exotic bazaars and watches people going about their daily routines.
One of the liveliest places in town is the area near the New Mosque in Eminönü. This area is a crossroads for commuters using the nearby bus and ferry terminals, for people going to the mosque or the Spice Bazaar, and vendors offering a wide assortment of items for sale. Dodging the crowds in Eminönü are flocks of pigeons waiting for bird lovers to buy and scatter some seed.
Istanbul's many markets and bazaars always offer something new and different to see. The largest and most popular is the Grand Bazaar, a city of its own with thousands of shops that has been in business since shortly after the Ottoman conquest in 1453. It is quite easy to get lost in there! A more manageable market is the Spice Bazaar, near Eminönü, which despite its name sells many things other than just spices.
One day, after we had seen enough of the standard tourist attractions for a while, we wandered from the Sultanahmet neighborhood (near the spectacular Sultan Ahmet (Blue) Mosque) down to Kumkapı, an area near the Sea of Marmara that specializes in seafood restaurants. Along the way we passed through a residential neighborhood with no listed tourist sites, but lots of activity as kids were playing in the parks and streets and men gathered to discuss the issues of the day.
One walk that should not be missed is a stroll across that Galata Bridge that spans the Golden Horn from Eminönü to Karaköy in Istanbul's Beyoğlu district. The bridge is lined with fishermen trying their luck (I only saw rather small fish among the catch) and, of course, vendors selling items the fishermen or others might need. On the lower level of the Galata Bridge is a string of restaurants, where one can relax and enjoy wonderful views across the Golden Horn.
Moving further north in the Beyoğlu district, one finds İstiklal Caddesi, a grand, pedestrian-only boulevard that runs from Karaköy to Taksim, one of Istanbul's most modern areas and home to many businesses and large hotels. Along İstiklal Caddesi are many of the city's upscale shops, chic restaurants and hottest night clubs. It's a great place for a stroll and people watching.
Another upscale area that gets very active in the evening is Ortaköy, which is along the Bosphorus in the shadow of the bridge that links Europe and Asia. There are so many restaurants in the area, many with water views, that it is hard to choose which one to patronize.
So, if your schedule permits, make sure to get out and just wander around. Istanbul is one of my favorite cities. The people are friendly, it is easy to get around (especially with the modern tram that runs between Sultanahmet and Beyoğlu), there are colorful shops and inviting restaurants everywhere and the views can be magnificent.