Prison island is about 5km off the main island of Zanzibar was uninhabited in the 1860s when Sultan Majid bin Said gave it to two Arab Salve owners who used it for imprisoning their slaves, as most who came from the interior of Africa could not swim. Apparently Zanzibar had the largest slave market in East Africa. Troublesome slaves from the market were moved to the island instead.
Slavery was outlawed in 1890, and then when the British took over in 1891 they repurposed the island into a health facility for quarantining visitors who may have cholera and yellow fever patients. Afterwards a small resort was built on the island which is currently being renovated…
but it’s good for a day trip, there’s a small museum, pizza restaurant, turtle sanctuary and excellent swimming.
The original entrance onto the island, including a small concrete shower base for washing quarantine patients.
The museum was well set up with clear explanations for each picture.