Built in the early 1940s to provide power for America's industrial needs during WWII, Fontana is the tallest dam east of the Rockies. At 2365ft wide, it's an engineering marvel – and all the more impressive given it was completed in just three years. Water released from the 29-mile-long reservoir (an impoundment of the Tennessee River) plunges down a 480ft tunnel to spin three massive turbines, which in turn generate enough electricity to power 290,000 homes.
A visitor center provides details of the construction – the nearby Fontana Village Resort was once the barracks for the thousands of workers brought in to build the dam. You can walk across the dam for fine photos above – indeed the Appalachian Trail goes right along the top. Even better views await at Shuckstack Tower, a strenuous, 4-mile (one way) hike from the dam.