I just uploaded my December SketchUp project to the Math Forum. This is a really neat logic puzzle, in which you start with a grid of "buildings" (or tall boxes).
You show only certain views of the model (front, left, etc.), and compile enough data to figure out which buildings have which height.
It's a little like Sudoku, but much more colorful! It's free, so check it out.
Anyone can design anything in 3D! www.3dvinci.net