So the trip to Gold Reef City ended up being postponed by only one day. Gold Reef City, is the only tourist attraction I knew off in Johannesburg, before I actually came here; mainly because of the "go down the mineshaft" tour option. I did not really know that it was also a theme park until very recently.
It is actually a very interesting theme park, and I think, over all, better than Ratanga Junction in Cape Town. The main roller coaster - Anaconda - is quite scary, and very impressive. But all of the roller coaster rides are interesting - especially the Golden Loop - which is the first roller coaster I have ridden that goes backwards. But I did not go to the really scary ride - the Tower of Terror, which features a vertical drop of about 40 metres. The queue was long, and I really did not feel like it, when I got there towards the end of the day.
As for the underground, mine shaft tour - it was certainly very interesting. The tour takes place in a real gold mine shaft, about 250 metres below ground, featuring the technology and techniques of gold mining. The shaft features many original implements and technologies, including a 100 year old AC-DC converter in the underground electric substation.
At R110, it is a bit on the expensive side; but there is a lot of other attractions including touristy attractions such as traditional dancing, live bands, restaurants (though quite overpriced) theatres etc. And, it is a load of fun.