obama today an emotional visit to robben island. That's the prison where nelson mandela spent most of his 27 years behind bars. President obama spending a few moments alone in that tiny prison cell.... See More
obama today an emotional visit to robben island. That's the prison where nelson mandela spent most of his 27 years behind bars. President obama spending a few moments alone in that tiny prison cell. Visiting that site, the president said, humbled him. The people who faced down injustice and rep fused to yield. Abc's chief white house correspondent jonathan karl, traveling with the president. Reporter: A desolate speck of land five miles off the coast of south africa, robben island is a police with a grim, cruel history. With a former inmate as their guide, the obama family toured the old prison that confined nelson mandela and others that dared to fight against apartheid. They viewed the quarry, where the prisoners were forced to labor, endlessly breaking big stones into small ones. Silently, the president stepped inside the cell, about the size of a broom closet, where mandela spent 18 years of his life. During those years, a young white guard was assigned to mandela, and the two would become unlikely friends. Years later, that guard talked to abc's david muir, remembering the time mandela's wife visited with their new grandbaby. She said, please, can I just showman della from a distance? I said, no, no, just leave the child. Reporter: No children alloweds, not even mandela's precious new grandbaby. What winnie mandela didn't know was that while she waited in a holding area, the jailer secretly brought the baby to see mandela. I saw tears coming out of his eyes. And no one ever knew? Nobody knew. Reporter: Now, with an ongoing vigil outside his hospital, mandela clings to life. Obama has spoken of him at every stop. Nelson mandela showed us that one man's courage can move the world. And he calls on us to make choices that reflect not our fears, but our hopes. Reporter: Although president obama did not get to see mandela, he did receive a warm welcome from another aging hero of the anti-apartheid movement -- bishop desmond tutu. Your success is our success. Your failure, whether you like it or not, is our failure. We pray for you to be great success. Reporter: At the end of his tour of robben island today, the president wrote an inscription in the guest book saying, quote, the world is grateful for the heroes of robben island. Who remind us that no shackles or cells can match the strength of the human spirit.
This transcript has been automatically generated and may not be 100% accurate.