This isn't a gadget—and it's even a couple of years old—but we think you'll forgive this weekend foray into "Oh, wow!" engineering. This bit of concrete and steel is the Falkirk Wheel, a boat lift connecting two canals near Falkirk, Scotland.
Thanks to Archimedes' principle (floating objects displace their own weight), each water-filled caisson weighs the same amount. That allows the entire counter-balanced tip to bring boats—water and all—up or down to the next canal using just a 1.5 kilowatt-hours of energy—the same amount of energy it takes to boil eight kettles of water.