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Photo: Fancy-cats-are-happy-cats, Attribution via Wikimedia Commons
The Cascade Locks and Canal was a navigation project on the Columbia River between the U.S. states of Oregon and Washington, completed in 1896. It allowed the steamboats of the Columbia River to bypass the Cascades Rapids, and thereby opened a passage from the lower parts of the river as far as The Dalles. The locks were submerged and rendered obsolete in 1938, when the Bonneville Dam was constructed, along with a new set of locks, a short way downstream.
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The third highest hydropower project in the US, at about 1.2 MWatts. Accessible via exit 40 on I-84, you can visit the dam (after passing a friendly guard who will inspect your car) as well as a fish ladder installed by the Army Corps of Engineers. Salmon run in the river almost year-round, but the fall is peak season.