Devil's Island, once the world's most notorious penal colony, is located off the coast of what country?

The penal colony of Cayenne or The Cayenne's Prison, was a famous prison of the 19th and 20th century. It operated at several locations in French Guiana. Opened in 1852, it was notorious for being used for internal exile of French political prisoners during that period, the most famous of whom was Captain Alfred Dreyfus. It is also known for its harsh treatment of criminals, who were deported there from all parts of the French empire. The system was closed down in 1953.

Prisoners convicted of felonies in the 17th and 18th centuries were sentenced to serve as oarsmen in the French Mediterranean galley fleet. Given the harsh conditions, this was virtually a death sentence. Following the decommissioning of the Mediterranean galley fleet in 1666, the majority of prisoners were paired together in chains aboard galley hulks(bagnes) moored in French harbours until the bagnes rotted and sank. The prisoners were moved to live on the adjacent pontoons. Prisoners relied on charity or their families for food, bedding and clothing. They were required to work 12 hours a day in the docks, earning 10-15 centimes, which they could spend on food and wine. Other prisoners were housed in prisons onshore, where conditions were apparently so bad that many prisoners would "beg" to be transferred to the hulks.