You don't have to go far to find Istanbul's treasures. Many are situated walking distance from the ship via the Galata Bridge on the Golden Horn, a freshwater estuary of the Bosphorus. With your guide in the lead, you'll stroll to Sultanahmet, the oldest part of the city, and the location of some of its most historic sites such as Yeni Camii, also known as the New Mosque. Located on the water's edge, it's a defining feature of Istanbul's skyline. Boasting 66 domes and semi-domes and two minarets, an elegant fountain sits in the center. Erected in the 16th century to honor the Venetian wife of Sultan Murat II and mother of Sultan Mehmet, it was built as part of a complex that also contained a hospital, baths, fountains and the Spice Market. Most of these buildings are gone, but the market remains and you'll have free time to explore.