This is my take on the classic wooden snake puzzle. Purchased ones generally range in size from 2" cubed down to key chain size. This one is 4.5" cubed. Although time-consuming and somewhat mind numbing, it wasn't very challenging to build. However, you will need to pay attention to the build...

This is an easy project to make but pretty challenging to solve. You spin the blocks until you have solved the math problem on each of all 4 sides. I've included a short video showing how it works. Build Instructions and more details: https://www.instructables.com/id/Math-Snake-Puzzle/