Hours and hours of fun in this quality wooden building kit. From a wooden marble run to bridges to towers. No glue, no connectors, just gravity and imagination.; Contraptions are made simply by stacking the planks. No glue or connectors are used, just gravity. When children play with contraptions, they learn simple and complex science principles such as slope, velocity, force, momentum, balance and more. Young builders will begin to understand these concepts through hands-on, active experience, often without even realising it.