Dueces:
Some great mentions above already. As a skinny tire/original mtn. bike guy, many good ones mentioned and some missed. As a Wisconsin cyclist I’m more familiar with our state and living in the Northwoods the mentions by picklerick and Michael Saal can’t be missed treasures!!! And Kirk Charipar’s mentions are exception places to bikes as well!!!
The largest non-trail opportunities exist on the paved county road systems of southern MN/WI that haven’t been talked about above. Originally from the Madison area, I used to ride to a local community approximately 20 miles away and look over county road routes to do, then ride there and return to my home of Cambridge. Generally not a lot of traffic and paved, the only issues were resurfacing of the roads that occasionally took place using pea gravel. The changes in rides were variable every trip!!!
Lastly my next door neighbor and Birkie and Fat Tire Festival friend Phil Van Valkenberg wrote 7 books on places to ride in WI and I highly recommend any of them for ideas:
https://books.google.com/books?id=JZ-lSQAACAAJ&source=gbs_similarbooks
Good Luck, reach out to me if ya want; and my wife and I are getting back into this summer.
Mark