From crossword games to brain teasers, most kids love puzzles. For the ultimate challenge, try a 3D wooden version. They’re sort of a cross between jigsaw puzzles and a toy construction set, combining Rube Goldberg intricacy with the joy of building something that works. These three-dimensional projects teach mechanical principles, woodcraft, and lasting patience. The finished product is a display-quality art piece that will bring hours of hands-on enjoyment both during and after construction. Here are a few traits to look for in a good 3D puzzle.