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Hi Dave,
The Africa is rich in its natural landscapes and wildlife. If you are interested in wildlife the Namibia is the most appropriate choice for a traveler. The Etosha National Park (Namibia) and Kruger National Park (RSA) are among the largest wildlife reserve in world.
The Kalahari desert is really an attraction for the travelers in Botswana. The Kalahari Game reserve is also a great place for wildlife lovers.
For RSA the Durban itself with its wonderful beaches is a great place to visit. But Capetown is the most beautiful place here. A visit to South Africa is incomplete without visiting Capetown.
I visited Africa about 3 years ago with a volunteering group. I think you can find some organization on the Internet for your purpose.