Whoever thought untying knots could be so much fun? Improve your sense of spatial relations with Brain String Advanced, a fun puzzle that, like all good logic games, is strangely addictive. It's a tetrakaidecahedron (14-sided geometric solid) with colored elastic cords running through the middle of it. The goal is to get cords of the same color each surface without any tangles in the middle. As you can see in the video below, it isn't easy.
This puzzle is a great tool to improve spatial reasoning, plan several steps ahead, and think through what unintended consequences an action may trigger. It can be solved by lots of trial and error, but in the process, you begin to see more and more steps ahead in untangling the knot.
My ten-year-old son received this puzzle from his grandparents, and we have been fighting over it ever since.