Topkapı Museum is the big one... the most important museum of Turkey and the Balkan Peninsula. It is an incomparably rich treasure-chest, brimming with things of historical importance. First, second, third and fourth courtyards; the Audience Hall, Divan-the High Court, Historical Kitchens, Royal Stables, the Treasury, gardens, kiosks… Probably the best commentary on Ottoman History, art and its culture is simply to come direct to the First Courtyard of this amazing Palace.
Next place to see is Hagia Irene Church (from outside). Our final places of interest are Caferaga Medrese and Sogukcesme Street. To see these things with a great guide... well, you will never be quite the same again.