This thing is called the Antikythera Mechanism, and according to the IPOD entry was found at the bottom of the sea aboard an ancient Greek ship, thought to have sunk around 80 BC. It's an analog computer used to predict the motion of the planets, sun and moon, and display the results on a clock-like face. It even predicts eclipses!
No one thought such mechanical sophistication was possible back in 80 BC, and some have offered it up as proof of ancient alien contact. More likely it is proof we don't give those old Greeks nearly enough credit.
Anyway, as cool as all that is, it is not as cool as this: somebody made one out of Lego! Not an exact replica, as is uses, according to the video, twice as many gears as the original. But still. For a discussion of some of the math involved, skip to about halfway through the clip.
