US President Barack Obama and first lady Michelle Obama tour the jail where Nelson Mandela was imprisoned on Robben Island, near Cape Town, June 30, 2013. During apartheid, Mandela spent several decades as a political prisoner on Robben Island. Obama visits a bleak former prison island off the coast of South Africa on Sunday to pay tribute to ailing anti-apartheid hero Mandela and set the stage for a speech urging Africans to strive for prosperity and democracy. [Photo/Agencies]

US President Barack Obama tours the cell block on Robben Island where Nelson Mandela was held captive near Cape Town, June 30, 2013. [Photo/Agencies]