The Hagia Sophia is, simply, the most spectacular building I have ever seen. The volume of the interior space takes your breath away, and the walls breathe history. In spite of it´s size, the interior is bathed in a soft light that is so different from many later European cathedrals. Built in the 5th century, it served as a Byzantine or Roman Catholic Church until the 15th century (that´s right, 1000 years!) when Istanbul was conquered by the Sultan Mehmet. The building then served as a mosque until 1935 (that´s right, another 400 years!), when it was secularized by Mustafa Kemal Ataturk, the founder and first President of the Republic of Turkey. Now, it´s an awe-inspiring pleasure to be able to stroll around inside this monumental space and see all of the beautiful architecture and decorative touches from both Christian and Islamic traditions. Impossible to describe accurately, hard to truly fathom from pictures, but an absolute must-see experience for anyone visiting Istanbul. It´s on my personal list of the 7 Wonders of the World!