Sphereing (or zorbing) is the practice of humans traveling in a sphere, generally mae of transparent plastic, usually for fun. Sphereing is generally performed on a gentle slope, allowing the rider to roll downhill, but sphereing can also be done on a level surface, as well as on water, permitting more rider control. In the absence of hills, at least one vendor has begun constructing metal ramps. Most spheres are constructed for a single rider, but some hold two or three. The longer runs are approximately half a mile.