Kwame Nkrumah Memorial Park
Where Ghana declared independence, and where its first president is buried.
The mausoleum and museum sit on the ground where Kwame Nkrumah declared Ghana's independence in 1957. The museum holds his personal effects, photographs of him with Nasser, Castro, Malcolm X and Du Bois, and the original statue toppled in the 1966 coup.
It is central, it is quick, and it gives you the political spine of the country in about an hour. Worth doing early in a trip rather than late, because a lot of what you see afterwards makes more sense with it behind you.