While there are a plethora of amazing things to see across the continent of Africa, the Victoria Falls really does rate right at the top of the pile.
Mosi-oa-Tunya - The Smoke That Thunders. The Falls have been known to African tribes for centuries, and were first discovered by European explorers when Dr Livingstone made one of his great trans-Africa expeditions in the 1800's. The story goes that upon hearing the Falls (which you can do from 20km away), and seeing the huge spray coming from them, many of his African porters fled in fear!
But these days, rather than fleeing, people flock to the Falls, to see this awesome wonder of the natural world. The Falls are about 2km wide, and drop around 100m into the gorge below.
The Falls form part of the border of Zimbabwe and Zambia, and so can be seen from both sides. From the Zimbabwe view points, you can get a much better feel for the great expanse of the Falls, but in Zambia, you can walk out onto 'the knife edge', a sliver of land that stretches right into the centre of the Falls, thanks to a small connecting bridge, and so get a real feeling of complete immersion in the Falls.
When I've been most recently, we were in Zambia, so I'll recount the Falls from that side. As you walk through the park to the pathway along the front of the Falls, all you can hear is a great roar, as the Falls drop into the gorge below. The first sighting of them is at the very top end of them, looking right across their face. Of course, you can't see even close to the other end, due to the huge amount of spray coming up. Walking around the area, you will inevitably get wet, but never more so than on the connecting bridge out to the knife edge. We ran across this bridge, and by the time we got to some resemblance of cover, we were thoroughly drenched to the bone! There is just so much water in the air.
There are numerous viewing points of the Falls - on the ground, you really can't grasp all of them at once, they're just so big. We have wide-angle photos that are simply a wall of white-water, looking across a very narrow gap (maybe 40-50m) to the water wall. To grasp the imensity of the Falls, you really need to go into the air, and see them from above.
As you come back out of the Falls, there is a craft market with some great curios, and they are generally quite good prices, too.