Hagiasofia or Ayasofya Mosque(after 1453), whateve...

Hagiasofia or Ayasofya Mosque(after 1453), whatever you name it. It is one of the greatest architectural magnum opus in the world and has whitnessed hundreds of years of 3 big empires which ruled the world in their times.
From the first step in, you will be inspired with the greatness of the building and the details will capture you and take to those empires, since every empire and even every king or sultan has left his signature to the building in a way where you will observe it.
I recommend you to read a lot about the history of Ayasofia, then visit it, so you won't miss the important details. Or a guide will be helpfull.
If you have a list of "places to visit", put Ayasofia on the top of the list.