Nice sport climbing (and trad so they say, I saw some good looking lines but didn't have any of my gear) in a pretty setting and easily accessible from Johannesburg and Nelspruit. The rock is sandstone and tends to be vertical to overhanging, though there are slabs too. When you get there, go to Rock N Rope (drive down the main street, it will be located on your left after a small bottle shop on the far end of town). Rock N Rope is the place to get all of the info for climbing and lodging/camping. I rented all of the gear that I needed to sport climb and they let me use a guidebook for free. This is the place to reserve campsites or a room in the climbers lodge. The climbers lodge is pretty awesome, I recommend it (actually the campground is awesome too).
There are two main climbing areas - basically across the highway by the waterfall and uphill from town. Both offer nice routes, although the ones by the waterfall are longer. Rock N Rope will drop you off at the waterfall climbing areas instead of leaving your car there because it is near the township, and therefore your car might get broken into. You then walk back from the crag (note: the waterfall crag that I went to requires that you climb back out of the gorge, no walk out). I wouldn't worry too much about the danger of the township, crime is the national obsession in SA, and people told me that they haven't ever heard of climbers getting into trouble. Just be aware, as you always should be in Africa.