Johannesburg is the largest city and economic heart of South-Africa. People are starting to make it a "friendlier" city, away from the bad name of robbers and thieves. You still need to be careful, but a city tour to see the old and new Joburg is certainly worthwhile. Buying diamants? De Beers has its HQ here. Politics? Visit So-We-To (South-West Township) where Nelson Mandela lived.
The Kruger National Park is one of the largest game reserves in the world. The big five and many other animals have their home here. The location north-east of Johannesburg makes it an easy destination.
Capetown ("Kaapstad" in Afrikaans) is one of the most beautiful major cities in the world. It is the meeting point for two oceans with mountains and a natural harbor. Thanks to its nature many migrants moved there and movies were recorded there. Activities may include surfing, fishing, shark watching (!) or just walking and enjoying. Note that the area also produces good wines...
Addo Elephant National Park is a diverse wildlife conservation park in South Africa and is one of the country's 20 national parks.
Bloemfontein (Dutch: "Flower Fountain") is one of the three capitals of South-Africa and a major city. This could be a major connection or a stop for wine-drinking or ostrich riding.
Durban is the 3rd largest city and the busiest port in South-Africa. Durban is a ethnically diverse city, with large Zulu, White, and Indian/Asian populations.
Hermanus is a city on the South-Coast where you may watch Whales from the coast, without the need for a boat, when the season is right.
Kimberley is important as a Diamond Mining area.