The 17th Century Cape Coast Castle overlooking the Atlantic Ocean in Ghana is a testament to man's inhumanity to his fellow man.
A few metres below where I am sitting, thousands of black African captives were kept in conditions that make me shudder even to imagine.
They were chained, naked and hungry in hot filthy conditions - waiting for slave ships that would cart millions to a life of degradation and humiliation.
As I went below into the darkness of the cells, those who came through here whispered stories to me in the silence - women clutching crying babies, groans of pain, and tears, yes, so many tears.
I saw the faces of those dragged and whipped, kicking and screaming through the door of no-return into the belly of a slave ship.
The window provided the only light for the captives below
This is a desolate, dark, miserable place.
I have been to the Cape Coast Castle before and it is always traumatic.
But in this place of human shame there is a light.
It is a tiny square in the corner of the high wall that the architects of this place provided to ventilate the thousands they so insensitively crammed into this dungeon - through it a single powerful stream of light shines.
No ordinary visitor
Two centuries after the first major attempt to end the slave trade, another visitor with an African father and a white American mother will stand close to where I am and perhaps battle with the same emotions.
But he is no ordinary visitor - Barack Obama is the 44th president of the United States.
Coming to Ghana is, for many African Americans, the equivalent of a spiritual journey
He is the man who is widely seen to embody the hopes a generation of black, white, Hispanic and Asian people around the world.
The people of Ghana are extremely excited about President Obama's arrival.
His pictures are everywhere. Songs have been written in his honour.
His choice of Ghana is significant on many levels.
Ghana was the first black African country to attain independence from British rule in 1957 - an inspiration to others across the continent.
At the time, many African Americans, burdened by segregation and discrimination, looked to Ghana and its founder Kwame Nkrumah as a beacon of hope.
The story is told of Vice-President Richard Nixon - the US guest of honour at our independence celebrations - who greeted a well-dressed black man with the question: "So how does it feel to be free?"
The man replied: "I don't know... I am from Alabama."
The local papers have been running pictures of a young Muhammad Ali and Martin Luther King celebrating Ghana's independence.
Coming to Ghana is, for many African Americans, the equivalent of a spiritual journey so common to all faiths.
Many Ghanaians are excited about President Obama's visit
Generations of African American doctors, lawyers teachers and educators still call Ghana home.
At independence, Kwame Nkrumah declared that this was "Our chance to show the world that... the black man can manage his own affairs."
Decades later we are still struggling to prove it.
The frustration runs deep across Africa, from Ghana through Nigeria to Kenya and Zimbabwe.
Contemporary politics does not take notice of something as vague as the word "hope".
The Obama presidency will be measured by how he deals with a global economic crisis, the threat of terrorism and the spiral of environmental degradation.
It would be naive for Africans to assume that the election of Barack Obama means an economic windfall for the continent or that the president does not have a strategic interest in securing this region's oil.
Bill Clinton and George Bush both came to Ghana during their presidencies.
Nonetheless, the emotion involved with the arrival of Barack Obama is immeasurable.
What Barack Obama represents is that "thing" - the thing that Maya Angelou says "Makes the caged bird sing."
I see it in the faces of young girls from northern Ghana who carry back-breaking loads for a few cents in the markets clutching dreams of owning their own business.
I see it in the face of the taxi-driver who works extra hours so his children can go to a better school than the one he attended.
Pupils in Ghana look forward to an 'historic' event
I've seen the same look on the face of a young doctor at Korle Bu teaching hospital who is overworked and underpaid and still delivers some of the best medical practice in Africa.
They do not want a handout, they just want a fair chance to achieve their potential.
That look is called "enyidaso" in the Akan language of West Africa.
It is the light that shone hundreds of years ago on the tear-stained faces of the human beings who passed through the Cape Coast dungeons.
Barack Obama calls it "hope."
Komla Dumor presents BBC World Service's The World Today programme. Born and raised in Ghana, he worked for Accra-based Joy FM, Ghana's leading commercial radio station before joining the BBC.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.