Going-to-the-Sun Road, Montana - completed in 1932, National Register of Historic Places in 1983, a National Historic Civil Engineering Landmark in 1985. The road is a spectacular 50-mile, paved two-lane highway - the only road that spans the width of Glacier National Park east & west, crossing the Continental Divide at 6,646-foot-high Logan Pass. It passes through almost every type of terrain in the park, from large glacial lakes & cedar forests in the lower valleys to windswept alpine tundra atop the pass.
Also on my bucket list. I should set up a Facebook road-trip donation page, lol!