This large rock allegedly marks the spot where the infamous 'Dr Livingstone, I presume?' encounter between Livingstone and Stanley took place on 25 November 1871 (Ujiji in Tanzania has a much better claim to being the location of this event, though). Wherever it was, this is as good a place as any to do your own re-enactment, though it'll probably be a solo performance as it's not too likely that you'll meet another tourist here.
A taxi from the city costs a rather excitable BFr40,000 one-way.