I'm sure a lot of you have already tried/done it, but this is for people REALLY bored or confident.
www.notpron.coman internet riddle game consisting of 81 levels (not to mention the negative levels afterward), you'll have to utilize EVERY computer skill you know to solve this game. The game's spoiled if you use a walkthrough tough, but the designers constatly change the game around to prevent a perfect guide.
Have fun