The Kondoa rock art site has been thoroughly reviewed already. Two things I would like to add. Firstly I found the entrance price quite steep. We were coming with our driver from Dodoma and not only had to pay for our own entrance fee, but seperatly for the car, our driver and the guide, which totalled 93.000 TSH ( around 40€). 
A second, more interesting point is that the Rock paintings have only suffered from wheather related causes, mainly rain seeping through the rocks, but not from human causes. The reason for this is that even nowadays, thousands of years after they were made, they still play a role in religious practices. Just below the B1 site there is a rock with a hole underneath, were according to the locals a deity lives. We saw people entering the cave, and if the deity approved the goat and chicken they brought with them would be slaughtered. It was my first visit to a WHS were i could witness the preparation for an animal sacrifice.