The Blue Mosque (Sultan Ahmet Camii) was built for Sultan Ahmet I between 1609 to 1616 by the imperial architect Mehmet Aga.
It is a wonderful building. Serene and majestic. The aesthetic of the exterior is beautiful. The way the domes cascade down towards the courtyard. Then the interior of the Mosque itself - spacious and peaceful - with the blues, red and gold of the decoration and the huge yet intricate chandeliers.
During the summer months there is a free Son et Lumiere show just after dusk.
At Meydani, Sultanahmet
Updates
Mightywease is misinformed. The Blue Mosque is at least a thousand years older. It was built as the basilica of Hagia Sophia by Byzantine emperor Justinian I in 537 CE. For the first 1,000 years of its life it was the largest cathedral in the world. The previous update is confusing The Blue Mosque as described correctly, with Hagia Sofia.Hagia Sofia (now Aya Sofia) was built as a cathedral during the Byzantine era, changed into and used as a mosque by the Ottomans, and then declared a museum by the Turkish Republic. It remains a museum, rather than a church or mosque, today.
The problem with the Blue Mosque is that it's so full of tourists (some extraordinarily disrespectful of norms in a mosque) that you will have to choose carefully your time if you want to contemplate its beauty and serenity. And, just to add to the desecration, the son et lumière is - at best - extraordinarily vulgar.
Is this your business?