1 December 1999
Robben Island is located off the coast Cape Town and was named as such by Dutch explorers who encountered many seals on the island. It was however, discovered in 1488 by the Portuguese explorer, Batholomeu Dias. When the Dutch colonized South African in the 17th century, the island was used to isolated people that were considered unwanted elements in colonial society. Among the first inhabitants were political leaders from the East Indies, who were imprisoned on Robben Island as they protested to Dutch rule of their countries. When the British took control of South Africa, a leper colony was started on the island. Initially lepers could live there voluntarily, but in 1892, the Leprosy Repression Act was passed, forcing lepers to remain in Robben Island. Their number eventually rose to 588 in 1893. Rough seas have been known to characterize Robben Island, and since the 1600's numerous ships have been wrecked there. A ship that was laden with gold coins to pay the employees of the Dutch East India Company  (DEIC) sunk off the coast of Robben Island. The coins, said to be worth millions, remain at the bottom of the Atlantic ocean.  A lighthouse was eventually built on to warn ships of the rocks that surround the island that along with the violent surf, have caused the destruction of many vessels. Robben Island is most well known for the political prisoners that were kept there, by the Dutch and British colonists, but more especially by the apartheid government since 1961. Countless member of the liberation struggle were imprisoned there, most notably Nelson Mandela, who spent eighteen years on Robben Islands. Others include the current South African president Jacob Zuma, and members of the African National Congress (ANC) like Govan Mbeki and Walter Sisulu. Among the political prisoners on Robben Island during the colonial period were Sayed Abdurahman Moturu, one of Cape Town's first imams, and the Xhosa prophets, Nongqawuse and Maqana Nxele. On 1 December 1999, the United Nations Educational, Scientific and Cultural Organisation(UNESCO), named Robben Island as a World Heritage Site. This is because its history serves as a sad reminder of the turmoil in South Africa's past, but also the courage with which that turmoil was overcome. *The event is dated 2 December 1999 by a different source  
References

Safari.com, Robben Island, Cape Town, South Africa, from SafariNow [online], Available at www.safarinow.com [Accessed: 24 November 2009]| UNESCO. Robben Island, from UNESCO [online], Available at whc.unesco.org [Accessed: 24 November 2009]