The Sultanahmet district is Istanbul's historical heart, home to monuments that have shaped world history. The Hagia Sophia (Ayasofya), built in 537 AD by Emperor Justinian, served as the world's largest cathedral for nearly 1,000 years before becoming a mosque after the Ottoman conquest of 1453. Today it functions as a mosque (free entry, modest dress required) and its massive dome, glittering mosaics, and sheer scale continue to awe visitors.
Directly opposite, the Blue Mosque (Sultan Ahmed Mosque) is famous for its six minarets and 20,000 blue Iznik tiles that give the interior an ethereal blue glow. The Topkapı Palace, residence of Ottoman sultans for 400 years, houses incredible treasures including the famous Spoonmaker's Diamond and Prophet Muhammad's relics. The Basilica Cistern, an underground water reservoir built in 532 AD, creates an atmospheric underworld of 336 marble columns reflected in still water.
All these sites are within walking distance of each other.






