If you are looking for a way to take your sand castle building up a notch and don't find terms like hyperboloid or hebesphenorotunda too intimidating to contemplate, check out Will Webber's winning contribution to the Thingiverse S.T.E.A.M. Math: Build a Castle summer challenge. The files are available for free download on Thingiverse and include roller patterns, cookie cutter shapes, and bucket molds. These designs are sure to make your castle stand out from the crowd and are a great way to explore mathematical concepts with the whole family, all while having fun in the sand, surf, and sun. Check them out at 3DPrint.com: http://3dprint.com/93432/3d-printed-math-sand-molds/