Once the biggest cathedral in the world, the Hagia Sophia is considered the magnum opus of Byzantine architecture. Visitors say it is a must-see when in Istanbul and recommend taking a guided tour ...

Spread across two continents and between two seas, Istanbul is a city of empires past. The Hagia Sophia, Blue Mosque, Topkapi Palace, and Galata Tower are just some of the many historic structures ...

Turkey's Hagia Sophia will open to visitors outside prayer ... paved the way for it to become a mosque. The sixth-century Istanbul landmark's museum status - in place for nearly a century ...