Robben Island is an historic Apartheid-era prison that held black political prisoners,... (Associated Press) 
 
 RETRANSMISSION TO CORRECT SPELLING OF PRESIDENT'S FIRST NAME - U.S. President Barack Obama U.S. peers out from Section B, prison cell No. The president and his family visited Robben Island, where the anti-apartheid leader spent 18 years confined to a tiny cell, including a stop at the lime quarry where Mandela toiled and developed the lung problems that sent him to the hospital for most of the month. Later, Mr Obama wrote in the guest book in the prison courtyard: "On behalf of our family, we're deeply humbled to stand where men of such courage faced down injustice and refused to yield. 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," Obama wrote in the guest book in the courtyard, his U.S. Secret Service agents standing watch in the old guard tower above. After the tour, Obama visited retired archbishop Desmond Tutu at a youth center run by his HIV foundation before delivering what the White House has billed as the signature speech of the president's weeklong trip, an address at the University of Cape Town that will be infused with memories of Mandela. Obama met Saturday with members of Mandela's family, but did not visit the anti-apartheid icon, a decision the White House said was in keeping with his family's wishes. It was the same venue where 47 years ago, US Senator Robert Kennedy gave his famed "ripple of hope" speech, which gave inspiration to those fighting the racially divisive policies of apartheid rule and linked their struggle with that of the US civil rights movement. Nelson Mandela: Key dates 1918 Born in the Eastern Cape 
 
 Born in the Eastern Cape 1944 Joins African National Congress 
 
 Joins African National Congress 1956 Charged with high treason, but charges dropped 
 
 Charged with high treason, but charges dropped 1962 Arrested, convicted of sabotage, sentenced to five years in prison 
 
 Arrested, convicted of sabotage, sentenced to five years in prison 1964 Charged again, sentenced to life 
 
 Charged again, sentenced to life 1990 Freed from prison 
 
 Freed from prison 1993 Wins Nobel Peace Prize 
 
 Wins Nobel Peace Prize 1994 Elected first black president 
 
 Elected first black president 1999 Steps down as leader BBC History: Mandela's defiant freedom speech 
 
 Mr Obama also announced a $7bn (£4.6bn) five-year initiative to double access to electricity in sub-Saharan Africa, in partnership with African countries and the private sector.
– President Obama may not get to see Nelson Mandela, but he paid tribute to the apartheid icon today by visiting the bleak prison cell where Mandela spent 18 years of his prison term, reports the BBC. Writing in the Robben Island prison guest book that he was "deeply humbled," Obama praised Robben's "heroes, who remind us that no shackles or cells can match the strength of the human spirit." Mandela, 94, remains in critical condition with the very lung problems he contracted during his time in the prison. Obama moves on to the University of Cape Town later today, where the AP notes that he'll unveil a $7 billion, five-year initiative to double access to South Africa's power grid.