Taken from turkeytravelplanner.com

What's so blue about the Blue Mosque? Not much.

Istanbul's imperial Mosque of Sultan Ahmet I (Sultan Ahmet Camii) is called the Blue Mosque because of its interior tiles, mostly on the upper level and difficult to see unless you're right up there with them.

Forget the blue tiles! The mosque (built 1603-17) is the masterwork of Ottoman architect Sedefkâr Mehmet Aga. It's built on the site of the Great Palace of Byzantium, on the southeastern side of the Hippodrome.

With its six minarets and a great cascade of domes, the mosque is a worthy sibling to Ayasofya (Hagia Sophia) just a few minutes' stroll to the north.