Excellent for developing balance and physical agility, this colorful set of river stones includes six pieces in three different sizes. Each size has a different shape and slope, and they can be stacked to create a variety of heights. The stones measure from 9 cm (about 3.5") high for a single piece to 28 cm high (about 11") for a full stack, and can support up to 80 kg (175 lbs). The stones all have anti-slip rubber dots, lines or concentric circles on the surface, as well as around the bottom edge to keep them securely in place on hard or soft surfaces. The set comes in a handy carrying bag with a zipper closure.