I find the easiest route, for me, is the following:
From OR Tambo, take .the R24 (West), now renamed Albertina Sisulu.
The R24 West Merges with, and becomes, the N12 West.
Follow the N12 West, and bear left, onto the N3 (SOuth).
Keep to the second lane from the left, and take the M2 (West) which curves away to the right. This used to be called the Francois Oberholzer freeway... I was unaware the name was still in use.
Pass the city centre on the right, and keeping to the left, take the M1 (South). also known as the De Villiers Graaf motorway.
You can take Northern Parkway off the freeway, BUT:
I personally prefer not to take the Northern Parkway off the M1S, because once off the freeway, it becomes a little tricky, and it is easy to miss the next turn, across the traffic.
I prefer to stay on the M1S, and take the next exit... Xavier Street (M17).
Turn right at the traffic lights, and cross over the freeway.
Xavier street becomes Crownwood road.
Turn Right into Northern Parkway (M34). A short distance down the road,is the Gold Reef city Casino, on the right, and the Gold Reef City Theme Park and Apartheid Museum on the left.
Sunday should be free of traffic jams.
There may be some road maintenance, or construction going on, though, as this is often done at weekends, but should not be too much of a problem.
You will need to spend at least 2 to 3 hours in the Apartheid Museum, in order to do it justice.
Enjoy the drive.