Imperial Istanbul Half-Day Tour: Hagia Sophia, Basillica Cistern and Grand Bazaar. Get a glimpse of Istanbul's fascinating Imperial legacies on this half-day sightseeing tour with an expert local guide. First visit Hagia Sophia, once one of the largest basilicas in the world and now the second-most visited museum in Turkey. Venture below ground to the ancient Basilica Cistern, which once supported the Great Palace of Constantinople, and hone your haggling skills at the bustling Grand Bazaar, one of the world's largest and oldest covered markets where you can shop for jewelry, spices, leather goods and souvenirs galore. Book this Tour and Save 10% Off Imperial Istanbul Half-Day Tour: Hagia Sophia, Basillica Cistern and Grand Bazaar.