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If cities are what are most interesting to you, then I think I would built my trip around I-70. If you take I-80 to Salt Lake, then cut down to I-70 in Utah, and take that across Colorado. That will have lots of scenic beauty, several national parks that could provide a detour, and then you could stop in Denver, Kansas City, and St. Louis before going north to Chicago on I-55. It also has a number of ski towns, like Vail and Aspen in Colorado that could be worth a stop, and there are also a handful of college towns like Lawrence, Columbia, and Champaign-Urbana that could provide some entertainment along the way.