Hiram M. Chittendon Locks

This mechanical wonder is best known as the Ballard Locks; it sits on the channel that links Elliott Bay to Seattle's Lake Union and Lake Washington. Thanks to the tides, the bodies of water aren't at the same level, so the locks allow boats to pass by using a kind of water elevator. It's free to come visit and watch boats line up to be allowed into the chambers that fill with water to move them up and down—though good luck finding parking nearby.