Obligatory, when in Istanbul, is a cruise up the Bosphorus. We didn't have the best weather for this, but it's still an amazing waterway dividing Europe from Asia and studded with old palaces and forts. A major landmark is the 1348 Galata Tower.
In 1990, we climbed the tower for a view over the city, and below us were women washing carpets on a rooftop, underneath lines of laundry:
There's plenty to see along the Bosphorus, but my favorite things are the old wooden buildings sprinkled along the waterfront. Sadly, most are gone, as is the open space between buildings. This is some of the most expensive waterfront on earth now.
Here are a couple from 1990, now replaced by characterless buildings that could be anywhere:
Rumeli hisar is one of two forts built opposite each other to control the traffic along the Bosphorus. Built 1451-2 at the narrowest point on the strait, it has terrific views. These are photos from 1990, as we didn't visit the fort on this trip: