Today  there is a full day guided  tour which includes            St. Sophia (closed on Monday)  the cathedral built by Emperor Justinian in 537 which was the largest church in Christendom for a thousand years, the Byzantine Hippodrome with its various monuments including a 3500-year-old red granite obelisk brought from Egypt and erected here in 390 AD. The Ottoman Empire produced marvelous architecture and you'll see two of its finest works: Topkapi Palace (closed on Tuesday) , home of the sultans, and the famed Blue Mosque of Sultan Ahmet I. After all these visits, you'll venture into the labyrinthine Grand Bazaar.Transfer back to your hotel for overnight.