It feels a bit harsh as Bruce did the hard work, but @govner1 is correct, it's the World Heritage Site of Stone Town - the old bit of Zanzibar City. Surprisingly most of the historic bits are not that old, mostly dating to the end of the 19th century apart from the original 17th-century Omani fort. Friday marked the 60th anniversary of the union of Tanganyika and Zanzibar to form Tanzania.