At first sight, the floor appeared to be made of tightly packed grey earth. But to visit the slave dungeons of Cape Coast castle, a fortress built by the English on Ghana's coast, is to walk on human excrement.
It was the product of the thousands of slaves who inhabited the dungeons until they walked down the tunnel to British ships that ferried them to the New World. 'It was like a test; if you could survive down there for six to 12 weeks, then you were strong enough to be a slave,' said Robert Bentril, the Ghanaian information officer for the West African Historical Museum at the castle. 'The dead were brought out and thrown over the wall into the sea.'
Cape Coast castle was one of dozens of fortresses built by European colonial powers down the west coast of Africa in the 16th and 17th centuries to facilitate trade, some mineral, some vegetable, but much of it human. From the Senegal river to southern Angola, a distance of 1,300 miles, three centuries of slaving took around 20 million West Africans to the Americas.
Not all Africans were victims. Many local chiefs, eager for the tremendous profits made possible by the slave trade and for imported European products, filled the slavers' insatiable demand by raiding villages for captives.
Initially gold, still one of modern Ghana's principal exports, was the main attraction for Portuguese, Dutch, Swedish and English merchants - until independence in 1957, Ghana was known as the Gold Coast. But with the opening of the colonies in the Americas came increased demand for labour, and Africans, who could survive the adverse climates and were also skilled in tropical farming and mining, were ideal.
Forced labour had wiped out millions of the original Indian peoples of the Americas, and the Europeans could not do the work. So the job was left to Africans. Britain needed to kick-start the final drive from feudalism to capitalism. The men and women who walked in chains down that tunnel to the ships and survived the transatlantic journey became footsoldiers in Europe's industrial revolution.
For Africa, though, it was an entirely different story, from which the continent has never fully recovered. Whole villages lost their strongest and ablest young people, and the battles waged by local chiefs to obtain more captives spread instability throughout the coast. The trade also fostered an appetite for European goods that survives until this day, and an abandonment of local production - trends the English encouraged.
The logic was spelled out in a 1751 directive from the British Board of Trade to the English Resident of Cape Coast Castle: 'The cultivation of agriculture and promotion of industry among the Negroes is contrary to the established policy of this country, England; there is no saying where this might stop, and that it might extend to tobacco, sugar, and every other commodity which we now take from our colonies in the New World and elsewhere . . .'
It is said that no European ever entered the Cape Coast dungeons. The task of feeding the live slaves and dragging out the dead ones was left to Africans.
In the centre of the castle's parade grounds lie the graves of a governor, Captain George Maclean, and his wife, the poetess Letitia E Landon who died shortly after joining her husband in the early 19th century, once Britain abolished slavery.
Today, the view from the old governor's residence is of the gunnery wall, surrounded by ancient black guns and canon balls, and of excited young children playing in the violent surf at the castle's edge.
The entrances to the tunnel have long since been covered by bricks, though as the wine bottles and wreaths indicated, local residents still pass through the dungeons to pray at the shrine.
The Ghanaian government has been restoring many of the old forts as a national heritage, and 600 tourists a month visit the Cape Coast castle.
'There is a great difference when African Americans go down in the dungeons than when Europeans go. The African-Americans you can see feel very sad for their forefathers,' said Mr Bentril. 'We Ghanaians feel sorry, but it is history, and that is why we are trying to preserve the castle so people will remember.'