Johannesburg is considered the gateway to Southern Africa and, as such, most travelers never make it out of the Tambo International Airport before venturing on to the other great locations in South Africa, or nearby countries such as Zambia, Zimbabwe, Botswana, and Namibia. There are plenty of experiences in the area, however, begging for your visit. So schedule an extra day or two to enjoy this metropolis.
Johannesburg has a fascinating history that began under 150 years ago. In more recent decades, the rest of the world has witnessed the fall of apartheid which is the Afrikaans word meaning "separateness." When visiting, be sure to set aside time to visit Soweto which is the location of many protests and riots in the 70's as well as the location of the first townships in the country; a form of overtly separating races.
It seems that we're constantly in search of the "missing link" of evolution and one such discovery was made in 1947: Australopithecus africanus (nicknamed "Mrs. Ples"). The hominid is estimated at being around 2.3 million-years-old. Mrs. Ples is also considered the "most extensive discovery of a single hominid species ever found in Africa." See her at Cradle of Humankind which is 51-miles from the international airport.
The Apartheid Museum is a must-see in South Africa which details the history of the country, colonialism, and of course the birth of apartheid back in 1948. The content of the museum is emotionally heavy, for obvious reasons, but the trip is well worth it for a face into humanity (both horrors and triumphs alike).
Winter in Johannesburg is May to September when temperatures remain mild, dropping down to an average high of about 63F.
December to March mark summertime for Johannesburg, and the temperatures are quite moderate reaching a high of only 79F on average.