With Wisconsin mentioned..
You might consider the 4 Trail Tour. It's only 100 miles, but very scenic, all rail-trails(I think the Sparta-Elroy was the first rail trail conversion..if memory serves). It includes The Great River Trail, LaCrosse Trail, Sparta-Elroy Trail, The 400 State Trail. Starts at the north end in Trempealeau Wildlife Refuge(nice ride in there too) and ends in Reedsburg, WI. Also nice town-campground about mid-Sparta Elroy Trail in Wilton..every Sunday they put on a pancake breakfast next to the campground..good shower too..and swimming pool. The Sparta-Elroy did have some severe storm damage a couple years back..they're nearly done with the repairs.
Bike 4 Trails
https://dnr.wisconsin.gov/topic/parks/elroysparta
There's a shuttle available in Sparta..Speed's Bike Shop I think.
I imagine Door Dounty has been mentioned already.