If you're looking for a difficult challenge in life, try building a perpetual motion machine. But if you want an impossible challenge, try assembling one of these intricate laser-cut metal puzzles that are now available in Optimus Prime, Megatron and Bumblebee versions.
If you're unfamiliar with these puzzles, they start off as flat thin sheets of pre-cut steel, but hundreds of folds later you end up with surprisingly detailed models of everything from space ships to fighter jets. You don't need glue or solder either, just a pair of nail clippers, tweezers and 10 times the patience of Mother Teresa.
At $US12 each you're not out a small fortune when you get fed up during the build process (you will) and when finally complete you'll have a shiny trophy of your perseverance and newly-formed ulcer. [Vat19]