If you want to see as much of Johannesburg as possible in one go, then hop on the red open-top buses! There are two bus routes running throughout the city, the Red City Tour Loop and the Green Suburbs Loop, taking you around Johannesburg's main sights.
Hop on the Johannesburg Green Tour at the main departure point in Rosebank which heads out to the green suburbs around Zoo Lake, Johannesburg Zoo and the Military Museum. When you have reached Constitution Hill, you can switch to the Red City Tour Line and continue the journey.
The red line will take you to the city center, where you can hop off and visit the “Roof of Africa” viewing deck on the 50th floor of the Carlton Center, the James Hall Museum of Transport and the Apartheid Museum. The bus offers 7 stops, before returning back to Constitution Hill and ultimately back to Rosebank.