Robben Island, the place where Nelson Mandela was imprisoned for 18 (out of 27) years, has been a UNESCO World Heritage Site since 1999. It was used as a maximum security prison during South Africa's Apartheid era, and has since become a symbol of the strength and endurance of its political prisoners, and "the triumph of the human spirit, of freedom, and of democracy over oppression. " (Quote from UNESCO World Heritage site, citing reasons for its inscription.)
Robben Island has a long history, visited by the Khoi long before any Europeans arrived, it was named by Portuguese sailors for the plentiful seals (Dutch for seals = 'rob'). The island has also been known as Penguin Island. It was first made a place of banishment by Jan van Riebeeck in 1658, and has since served as a prison, a leper colony, and as a defensive station during World War II.