There are many places that claim to be the "Center of the World." As you might expect, the claims are generally ethnocentric. The ancient Greeks, for example, who thought very highly of themselves, erected a monument in Greece called the omphalos. It is Greek for navel (or belly button).
The Hagia Sophia in Istanbul doesn't claim to be the belly button of the world but it many ways it is. Because Istanbul has long been located on the major trade route between Asia and Europe, it became a melting pot of cultures. The Hagia Sophia is an amazing testament to the clash and then mixing of these cultures. Built on the site of a pagan temple, this basilica was first a Christian temple, then converted to an Islamic mosque. Because Islam prohibits representational art in its mosques, all of the mosaics in the dome were whitewashed. But in 1935 Mustafa Kemal ("Ataturk") decreed that the Hagia Sophia become a museum and evidence of both religions are clearly evident, including the Arabic writing and the beautiful mosaic decorations on the domes.
Photographically, this is a very difficult subject - in part because of how dark the interior is and in part due to the expanse of the interior, which my lens couldn't do justice to. You'll have to go there to experience this place in person.
View on Panoramio