Having traveled to Istanbul, I would LOVE to see an abandoned version of it, as the sun rises, or sets. Also, Constantinople in AC Revelations was excellent, and a very accurate rendition of modern day Istanbul.

You'll start in an abandoned Merchant's street, something like Taksim Square. You'd fight a large giant like a cyclops. Then continue towards something like Galata Tower and climb it, and teleport to a mosque, where outside a group of Ottoman Military soldiers will be (heck they can even be called Turks as a reference to FFVII), and you'll fight wave after wave. Lastly you enter the Hagia Sophia and explore it and the underground where the recently discovered Gate to Hell is. There you will fight an Ahriman like boss since the Evil Eye is so popular in Turkey (can just be called Evil Eye in Turkish).