The Boiling Pot is the churning basin below Victoria Falls, where the Zambezi gathers itself after the drop and forces its way into the first gorge. At low water the surface can look deceptively smooth; at high water it rolls with slow, heavy swirls that explain the name.
You can look down toward it from the bridge area, while closer access is usually from the Zambian side by a steep path. It is most interesting if you are already exploring the gorge and bridge, and it adds a physical sense of where all that falling water goes next.