Hello,
looking for ideas for things to do and see for a road trip from Milwaukee to Colorado for a couple of Seniors. Will take our time and we'll wing it when it comes to sightseeing and places to stay. Interested also in the Dakotas and then Vegas too. Thanks for any info or advice you might have for us.

Are you aware there is a "road trip forum"?
https://www.fodors.com/community/road-trips/

Moved to the United States forum and edited the title, adding "Milwaukee to Colorado "

It would be nice if you could explore the Black Hills en route to Colorado. The Black Hills are actually small mountains (7,242 feet is the highest point). There are lots of things to see and do there: Mt. Rushmore, Crazy Horse Monument, Wind Cave National Park, Custer State Park (a state park of national park quality with bighorn sheep and bison) and Roughlock Falls Nature Area is located in Spearfish Canyon.