If you leave the Haghia Sophia or Aya Sofia and turn left, then at the corner left again you’re on your way to the Topkapı museum. However, if you’d turn left again after some 30 meters, you’d find there is – after a period of restoration – another big attraction: the türbeler (mausoleums) of a number of sultans. My advice: take that turn, you’ll find a couple of very well designed buildings (at least one by the greatest Turkish architect Sinan), with wonderful decorations, in some with “Iznik” tiles from the greatest period of tile making. It's free of charge and definetely adds something extra to a Hagia Sophia visit. As a matter of fact, during the latter visit you may, almost leaving the main building, have turned left and seen a small baptistry area (see a series starting here . And through some window you can see people visiting one of the mausolea. But you'll have to take the route mentioned above to get in their position.