The Croton Dam

The Croton Dam is supposedly the second-largest hand-hewn stone structure in the world, after the Great Pyramid at Giza. Having misplaced our guide to the world's largest hand-hewn stone structures, we don't know if that's true, but the dam is indeed huge, not to mention a vital part of the New York City water supply system, with 19 billion gallons sitting in the Croton Reservoir behind it.