When visiting South Africa, it can be tempting to pass on Johannesburg altogether (aka Jo'burg, or Jozi amongst the locals). It has a reputation of being very dangerous, and lacks the natural beauty of Cape Town. Still, I found there was more than enough to do to keep me busy for a few days.
Most hostels are in the suburbs, as with any big city, there are legitimate reasons to be concerned about safety. I chose to hire a guide through my hostel, and went on two separate trips around the city with him. On the second one, his young son even joined us for lunch and a trip atop Africa's tallest building.