This full-day sightseeing tour of Istanbul provides a perfect introduction to the city that straddles Europe and Asia. When Istanbul was known as Constantinople, it was the capital of the Roman Empire and the wealthiest metropolis in Europe. On this city tour you’ll visit Istanbul’s 4 most important historic sites with a local guide. The Blue Mosque is an iconic monument in both the Turkish and Islamic worlds. The stunning structure was built in the classical Ottoman style, and features 6 towering minarets and 260 windows that provide illumination for its vast inner chamber that is lined with more than 20,000 Iznik tiles. In the 6th century, the Hagia Sophia was built by the Emperor Justinian. After the Ottoman conquest, it was converted to a mosque and later converted into a museum, featuring many beautiful Byzantine mosaics. One of the largest and oldest palaces in the world, Topkapi is the crown jewel of the Ottoman Empire. With its treasury and exotic buildings overlooking the Golden Horn, walking Topkapi's grounds offers gorgeous views of the city and the nearby Bosphorus. You’ll have time to shop at the Grand Bazaar – its 58 streets are lined with more than 4,000 shops. It is one of the world's largest covered markets, and is particularly known for its jewelry, leather, pottery, spices, and carpets.