The Large Hadron Collider. 17 miles, 11 billion dollars, and I don't know how many years later. Theoretically this behemoth is supposed to simulate the instant after the big bang, find out more about the Higgs Boson, and explain things like how matter have mass and what not. First phase of testing just got completed, and the fun, smashing part starts in October, if we're still around to see it. Oh, and this thing can create black holes, though the scientists say there's nothing to worry about.