Query: What iconic historic structure is in the center of old Hyderabad?
Context: Shahi tombs are other existing structures of this period. Among these the Charminar has become an icon of the city; located in the centre of old Hyderabad, it is a square structure with sides 20 m (66 ft) long and four grand arches each facing a road. At each corner stands a 56 m (184 ft)-high minaret.