For our Botswana Safari we flew into & spent a couple of days in Johannesburg. Created in the late 19th century as a result of finding gold in the area, Joburg feels an artificial city to a casual visitor, such as myself. It has no history and has wealthy areas showing off its "bling" next to very poor areas.
Personal safety is a serious issue here. Tourists are not advised to go out after dark. The hotel we stayed in didn't offer evening meals, so everyone had to order take-aways to be delivered. It was not safe to walk to the nearby shops in the evenings. In the full free day we had here we took a taxi to the start of a hop-on, hop-off city tour & a taxi back to the hotel at the end. On the bus tour there were areas where the commentary stated that tourists should not visit as we would find the experience overwhelming (in other words you would certainly get mugged!).
The only place we hopped off the bus was at the Apartheid Museum, which was one of the best specialist museums I have visited.