I love the idea of a magical jigsaw puzzle. Perhaps one made up of thicker, glass pieces that lock together (when put together, you know, like a normal puzzle would, only, so that it wouldn't fall apart on them). They could be given clues towards the beginning of the task, and would then be forced to use this clue to find each piece, and solve the riddle, which would work sort of like the goblet of fire did in the maze- the last thing that they had to gather in order to win.
Each location, however, would have to be different and would need to get more challenging for the champions as they went on to find the next piece. Meaning there would be as many pieces to the puzzle as there would be tasks, and that there would also need to be obstacles to prevent them from collecting said pieces- but would there be three pieces for each task, for each champion, so that everyone had the chance to collect all of the pieces? Or would there only be one per task, so that only one could win- this would make things more difficult for us, meaning that we could have to provide more tasks if one of the champions did not hold their position in the lead, and ended up screwing it up by losing a piece to another champion.
I'm just shooting ideas your way, Khaat. Feel free to absorb and/or ignore whatever information you please.