We flight from Addis Ababa, Ethopian to Guangzhou, China. During this flight we have 22 hours for transfer time in Turkey, this is a good chance to travel in Istanbul, Turkey. For me, it is a successful trip, the detail travel schedule as following:
Arrived turkey: 6:30am
We are successful pass the custom, because we applied E visa in advance by USD70 dollars per person. If you don't have visa, there have visa apply in the airport very near to custom, I don't know the exactly fee, but it is very quick
Take Havaist bus to Istanbul Center:7:30am
The bus is a big white bus called havaist, 20 minutes cycle till night 8:20pm, the round tickets is 36 TRY, no cash. You can buy them in the station, near the bus station.
It will takes you 1 hour. Then you will arrived Hagia Sophia, and the Blue mosque is behind of it.