There are a lot of attractions around the Old City of Istanbul or Sultanahmet and one of the first thing to see is the famous Ayasofya. Ayasofya was constructed as a church between AD 532 to 537 on the order of Byzantine Emperor Justinian. It is one of the greatest example of early Byzantine architecture and also traditional Roman architecture.
When Ottoman conquered Constantinople in 1453, Sultan Mehmet II ordered Hagia Sophia to be converted to Ayasofya Mosque and at that time 2 minarets designed by Mimar Sinan were added to the building. 2 more minarets were added later during the era.
When I strolled to Ayasofya from the park, I felt like I was approaching a ordinary, historical, huge Byzantine building. We have to line up (a long line) under the hot sun to buy tickets and I thought inside of this building must be packed like sardine. But, when I approach the entrance of Ayasofya, everything changes. Through the first door, we enter the second door and the third door and the great space beyond. The interior of Ayasofya is awesome and it is so big.
I can feel the cool air inside Ayasofya and I thought it was the aircond but I could not find any air conditioner, then I noticed that the pave, the pillars and all the surfaces other than the walls are from marbles, may be this give the cool atmosphere inside the building.When I looked up above, there are eight round green panels hanging in the central room written with the Names of Allah, the Prophet Muhammad, the four Caliphs and Hasan and Husin ( Prophet Muhammad's grandson).
Window details. 
The jar was made by a single marble and the lamps are the typical Ottoman oil lamps.
Panels written Allah and Muhammad. At the centre is the mosaic of Virgin Mary with Jesus 
The minbar and mihrab were added to Ayasofya after it was converted to a mosque. This minbar also is made of marble.
The Mihrab and two candle holders. 
One of the mosaics displayed at the upper gallery of Ayasofya. During the Ottoman era all the mosaics were plastered over.
We had to walk up the ramp for almost 5 minutes to the upper gallery which displayed all the mosaics. It was like climbing a small hill, very tiring but worth it. 
The massive dome of Ayasofya. The original dome from Byzantine era had collapse several times and during the reign of Sultam Selim II, Mimar Sinan designed this dome with 40 window panels around it and the dome is decorated by handwritten calligraphy of Surah An Nur. 
Luqman enjoying himself. 
For over 500 years Ayasofya remained the principal mosque of Istanbul until 1935, when it was converted to a museum by Republik of Turkey under the order of Kamal Attarturk.
Just across the street there is another impressive monument from Byzantine Era which the Basilica Cistern or known as Yerabatan Sarnici by local people. During the Byzantine era it was used as a reservoir for water storage for the palace and other buildings.
The interior of the cistern is breathtaking.
The walls of the cistern were built by thick bricks and there are 336 marble columns to support the cistern.
The ceiling gravity is distributed to the columns through the arches.
There are two Medusa heads used as the bases of two columns of the Cistern which are from the Roman Period. One of the Medusa's head is put upside down.
Based on the history, after the Ottoman conquest Istanbul, the gardens of Topkapi Palace were watered through this cistern. But the Ottoman preferred tap water to deadwater and they installed their own water system and abandoned the cistern. The cistern went a major restoration between 1985-1987 and was open to public after that.
.jpg)
