DAKAR, Senegal -- It was a brief moment, but a symbolically powerful one.

President Obama stepped alone into the frame of the Door of No Return on Senegal's Goree Island on Thursday afternoon, taking a look at the Atlantic Ocean from the same views that African slaves once did on their way to North America.

A photo of the moment shows the president wearing khaki pants and a white dress shirt, sleeves rolled partially up his arms, as he gazes at the ocean. He was later spotted asking questions of the tour guide, Eloi Coly, who showed the family around the former slave house, which now stands as a museum.

Speaking to reporters afterward, Obama called the tour a "very powerful moment" that helped him "fully appreciate the magnitude of the slave trade" and "get a sense in an intimate way" of the hardships slaves faced.

The trip was a reminder that "we have to remain vigilant when it comes to the defense of human rights," Obama said. "This is a testament to when we're not vigilant in defense of human rights what can happen. Obviously, for an African American, an African American president, to be able to visit this site, gives me even greater motivation in terms of human rights around the world."

The First Family took the tour after a day in which the president met with Senegal President Macky Sall and visited the nation's Supreme Court to emphasize the rule of law in democratic societies.

The Obamas traveled to Goree Island on a 73-foot boat called "La Signare," a blue-and-white ship festooned with Senegal's flag and a "Welcome President Obama" banner. The Secret Service and White House staff followed in a six-boat convoy.

They were accompanied by the Salls and met by a drum corps, some of whom wore T-shirts with the 44th president's face.