Unguja, also known as Zanzibar Island, is the main island in Tanzania's Zanzibar archipelago. Stone Town, which is part of Zanzibar City, is an ancient trade centre with mosques and winding lanes. The House of Wonders, built in 1883, is a former sultan's palace with a clock tower. The Old Fort is now home to a cultural centre as well as a stone amphitheatre. Underground aqueducts supplied hot water to the Hamamni Persian Baths in the late 1800s.