From the World Heritage inscription:
These fortified trading posts, founded between 1482 and 1786, and spanning a distance of approximately 500 km along the coast of Ghana between Keta in the east and Beyin in the west, were links in the trading routes established by the Portuguese in many areas of the world during their era of great maritime exploration. The castles and forts were built and occupied at different times by traders from Portugal, Spain, Denmark, Sweden, Holland, Germany and Britain. They served the gold trade of European chartered companies. Latterly they played a significant part in the developing slave trade, and therefore in the history of the Americas, and, subsequently, in the 19th century, in the suppression of that trade.
They can be seen as a unique “collective historical monument”: a monument not only to the evils of the slave trade, but also to nearly four centuries of pre-colonial Afro-European commerce on the basis of equality rather than on that of the colonial basis of inequality. They represent, significantly and emotively, the continuing history of European-African encounter over five centuries and the starting point of the African Diaspora.
I visited both the Cape Coast Castle and the Elmina Castle as part of my 2014 West Africa Cruise on G Adventures. The image shown is on the Elimina Castle.
The slave trade is one of the most significant and common historical themes which can be seen along the coast of West Africa. Millions of people were captures, almost always by other Africans, and traded to Europeans before being shipped off to work in New World plantations. The slave trade was so large that the area just to the east of Ghana was known as the Slave Coast.
The forts in Ghana are far easier to visit, and are better preserved, than the slave forts in other neighboring countries. Ghana has a better tourism infrastructure and has more resources to devote to cultural preservation. That isn’t to say they are perfect, but far better than their neighbors.
In addition to the forts themselves, the nearby fishing towns and villages provided an amazing opportunity for images of boats and fishermen.
I would consider the forts and the slave trade history to be a highlight of any visit to Ghana.