ROBBEN ISLAND, South Africa – President Obama and his family visited this historic island on Sunday, taking a solemn tour of the cell where Nelson Mandela was jailed for decades.

“We’re deeply humbled to stand where men of such courage faced down injustice and refused to yield,” Obama wrote in a guest book in the jail’s open air, dirt field, surrounded by high walls and barbed wire. First lady Michelle Obama watched him write the message and signed her name with his when he was finished.

 “The world is grateful for the heroes of Robben Island who remind us that no shackles or cells can match the strengths of the human spirit,” Obama wrote. Moments before he had seen the small, sparsely furnished jail cell where Mandela, 94, had been assigned before his release in 1990.

Mandela was jailed for his anti-apartheid protests; Obama has credited Mandela for inspiring his own political activism as a college student.

The president, first lady and their daughters also visited  the lime quarry where the political prisoners  did hard labor. They listened as an 83-year-old tour guide, who himself had been jailed on the island, described the meaning of the quarry.

Obama used the opportunity to tell daughters Malian and Sasha that Indian Mahatma Gandhi had begun his movement of non-violent protest in South Africa as a young lawyer.

“Here is where he did his first” activism, Obama said. “When he went back to India the principles ultimately led to India independence and what Gandhi did inspired Martin Luther King.”

After signing the guest book Obama put his arm around his wife and walked out.