If you're looking for a smart challenge...
If you have an hour to build something cool...
i give you....
A 3X3 Rubik's Cube, with Sudoku on each side.
Step 1: What you need
1. Rubik's Cube (can be old, or cheap, or just one you can ruin without regrets)
2. Stickers that you can write on
Step 2: Strip the Cube
Peel the color-stickers off
Clean excess glue and sticker-traces that's left (with solvent or detergent - just don't use a lot)
You'll end up with a bare cube, black plastic only.
(if you love your cube - solve it for the last time before you undress it..)
Step 3: Make Sudoku Stickers
2. Prepare 54 square Stickers (3X3X6=54)
maybe you can find ready stickers
I had to cut mine out from larger stickers
3. Make 6 sets of stickers with 1,2,3,4,5,6,7,8,9 on them (Sudoku is 1-9.. right?)
Don't forget to underline 6 and 9 to distinguish between them!
Step 4: Stick 'em Up!!
Stick a set of sudoku numbers stickers on each side of the stripped Rubik's Cube
(Make sure you stick them well - solving the SudoKube can become pretty violent!
And there you have it!! a home-made SudoKube!!
now...... just solve it!!!
(does anybody want to make an instructable on solving it?.... heh)