US preacher Roxanne Caleb blinked away the tears as she emerged from a pitch-dark dungeon where African slaves were once held before being shipped across the Atlantic to America.

"My mind still can't wrap around the fact that a human being can treat another worse than a rat."

Caleb is among the African-American visitors flocking to Ghana as it marks the "Year of Return" to remember the 400th anniversary of the first slave ship landing in Virginia.

Cape Coast Castle, 150 kilometres (90 miles) from the capital Accra, is a major magnet for those visiting

The white-washed fort lined with cannons was one of dozens of prisons studding the Atlantic coast where slaves were held before their journey to the New World.

The West African nation is banking on the commemorations to give a major boost to the number of tourist arrivals as it encourages the descendants of slaves to "come home."

A string of prominent African-Americans have headed to the site this year to mark the anniversary since the first slave landing in 1619.

Among them was a delegation of Congressional Black Caucus led by House Speaker Nancy Pelosi that toured last month.

Can't forget history

For those visiting it is an emotional rite of passage.

"This has been understanding my history and my roots where I came from," Caleb said.

"I am very thankful I came here as part of the Year of Return."

Tourists look inside the dungeons at the Cape Coast Castle, AFP

Sampson Nii Addy, a corrections officer with the Montgomery police department in Alabama, said he and his family had found the tour an "education."

"I think every black person needs to come around to learn history; how people were treated," the 52-year-old said.

"We can't forget history but we can always learn something from it."

Ghana, one of the continent's most stable democracies, has long pitched itself as a destination for African-Americans to explore their heritage and even settle permanently.

In 2009 President Barack Obama visited with his family and paid homage at the Cape Coast Castle.

Visitors gather, at Cape Copast Castle, outside the "Door of No Return." AFP

The "Year of Return" has added fresh impetus and the country is hoping it will increase visitor numbers from 350,000 in 2018 to 500,000 this year, including 45,000 African-Americans.

"It's like a pilgrimage. This year we've a lot more African-Americans coming through than the previous year," he said.

"I'm urging all of them to come home and experience and reconnect to the motherland."

Love to come again

Akwasi Awua Ababio, the official coordinating "Year of Return" events, pointed to high hotel occupancy rates as he said "enthusiasm is very high and we've got huge numbers coming from the US and Caribbean".

A tourist takes a pictures of the dungeons at the Cape Coast Castle. AFP

"Human resource is always an asset and we need to see how we can welcome them home to utilise their expertise and networks," the director for diaspora affairs at the presidency said,

The African American Association of Ghana brings together those who have moved to West Africa and offers help to integrate them into their new surroundings.

President Gail Nikoi praised the "Year of Return" initiative by Ghanaian leader Nana Akufo-Addo and said the country was "setting the stage for future engagements and involvement of African-Americans and other Africans from the diaspora in the development of this country."

But she said the authorities could still be doing more to help attract arrivals and convince them to stay.

"Dialogue and engagement is the first step," she said.

"It has broadened my horizons about how we came to be here and what our ancestors went through," said William Shaw, 57, from Montgomery.

"I would love to come again. There is a lot more to see here in Ghana... at least once in a year I'd advise African-Americans to come back to their native land and learn about their history."

Agence France-Presse