Most Taxing Game?

I was just wondering what the most taxing game you've ever played was.

I've been dicking around on Armor Games and I don't know if anyone else has ever played it, but this game Corporation Inc. has got my laptop all the way up to 3.1 ghz :p. I've got over 2000 employees all running around making me millions of dollars a day. Now graphically it's not demanding at all and my GPU is sitting at a comfy 60degrees Celsius. Processor though taxed isn't even running on more than 4 threads (cores)

SO what is the silliest, unexpectedly taxing game you've played?
For some reason I have to overclock the GPU to get Minecraft to run smoothly. I don't know why there's just something wrong with the game.

Minecraft requires a lot of power to load everything; it loads the entire world all at once, so it's a pretty taxing game! (imagine having to load every pixel of every texture of every block in a game that's roughly the same size as Great Britain...)