The president called it "particularly important for Malia and Sasha, who are growing up in such a blessed way, to be reminded that history can take very cruel turns," said the president, whose wife is the great-great granddaughter of slaves in South Carolina. "And hopefully one of the things that was imparted to them during this trip is their sense of obligation to fight oppression and cruelty wherever it appears and that any group of people who are degrading another group of people have to be fought against with whatever tools we have available to us."
The president said his tour of the three-story castle was "reminiscent" of his recent trip to the Buchenwald concentration camp in Germany "as it reminds us of capacity of human beings to commit great evil."
He called it "striking" that "right above one of the dungeons where male captives were kept was a church. And that reminds us that sometimes we can tolerate and stand by a great evil even as we think that we are doing good."
Loudspeakers had been set up outside the castle so the thousands gathered could hear the remarks of the first African-American U.S. president. Tens of thousands lined the streets to the castle from the landing zone where Obama's helicopter from Accra arrived.
Many wearing Obama T-shirts and chanting the president's name, Ghanaians cheered his arrival from rooftops, leaning out of windows, and hanging from scaffolding. At one moment, hundreds began chasing the motorcade until they were stopped by security.
"As Americans, and as African Americans obviously there's a -- there's a special sense that on the one hand this place was a place of profound sadness," said Obama. "On the other hand it is here where the journey of much of the African-American experience began."
At one point in his family's tour of the facility, the guide showed them the Door of No Return, through which slaves would pass, never to return to Africa again. Obama had his arm around his 8-year-old daughter Sasha, while first lady Michelle Obama held hands with 11-year-old Malia.
In remarks to children during February's celebration of Black History Month, the first lady noted that "African-American slaves helped to build this house" in which the first African-American first family of the United States now resides.
The president said today that "symbolically to be able to come back with my family, with Michelle and our children and see the portal through which the diaspora began -- but also to be able to come back here in celebration with the people of Ghana of the extraordinary progress that we've made because of the courage of so many black and white to abolish slavery and ultimately win the civil rights for all people -- I think is, is a source of hope."
The president seemed to be overcome with emotion as his made these remarks, pausing to collect his composure.
"It reminds us that as bad as history can be, it's also possible to overcome," he said.
The first family participated in the unveiling of a plaque now hanging outside the male slave dungeons that reads: "This plaque was unveiled by President Barack Obama and the First Lady Michelle Obama of the United States of America on the occasion of their visit to the Cape Coast Castle on the 11th day of July 2009."