ThinkFun Gordians Knot

Gordians Knot is the World's Hardest Take Apart puzzle… if you like a serious puzzle challenge, this puzzle is for you. The puzzle was designed using a computer and tuned to make the solution incredibly difficult. Gordians Knot was featured in an episode of NUMBERS -- it is that good. The puzzle comes with a visual instruction booklet that shows how to take it apart and how to reassemble it, for when you get stuck.