There are many activities in Zanzibar and places to visit and one of top spots and nearest would be the Prison Island. As you tour around Stone town, a lot of local guides and boatmen would offer you a tour in the Island but group tour packages are available in most hotels/hostels. Prices may vary so you have to ask a lot of people and make economical bargains.
Changuu Island (also known as Kibandiko, Prison or Quarantine Island) is a small island 5.6 km northwest of Stone Town, Unguja, Zanzibar. The island is around 800m long and 230m wide at its broadest point. The island saw use as a prison for rebellious slaves in 1860s and also functioned as a coral mine.
The British First Minister of Zanzibar, Lloyd Mathews, purchased the island in 1893 and constructed a prison complex there. No prisoners were ever housed on the island and instead it became a quarantine station for yellow fever cases.
More recently, the island has become a government-owned tourist resort and houses a collection of endangered Aldabra giant tortoises. These tortoises were originally a gift from the British governor of the Seychelles.
In 1919 the British governor of Seychelles sent a gift of four Aldabra giant tortoises to Changuu from the island of Aldabra. These tortoises bred quickly and by 1955 they numbered around 200 animals. However people began to steal the tortoises for sale abroad as pets or for food and their numbers dropped rapidly. By 1988 there were around 100 tortoises, fifty in 1990 and just seven by 1996.