... generally performed on a gentle slope, allowing the rider to roll downhill, but can also be done ... surface, as well as on water, permitting more rider control. In the absence of hills, at least ... metal ramps.Most spheres are constructed for a single rider, but some hold two or three. The ... a mile. Product:Zorb Ball, Water Roller, Water Walking Roller, Water Walker, Inflatable Water Roller, Water Rolling ...