I enjoy the countryside scenery along US-151 from Dubuque toward Madison. That's on your way to the Dells.
I agree that Peninsula SP is worth visiting at least, even if you don't stay there. I rented a bike just outside the entrance and pedaled in for free.
You might consider a visit to and a boat ride at either the Pictured Rocks (Munising MI) or the Apostle Islands (N of Ashland WI).
I really like the area north of Duluth, along Lake Superior from Two Harbors to Grand Marais. So many nice waterfalls, trails, and shoreline. There's a FHU municipal CG by the lakeshore at Grand Marais, if you can get reservations. From there you can day-trip to all the state parks along there as well as a drive along the Gunflint Trail (very wild and pretty). Be sure to see Split Rock Lighthouse as well as Palisade Head (the latter is an overlook about 200' above the lake). In Grand Marais, I recommend a pizza at Sven and Ole's, and then a stroll out past the coast guard station to Artist's Point.
Mike G.
Liberty is meaningless where the right to utter one's thoughts and opinions has ceased to exist. That, of all rights, is the dread of tyrants. --Frederick Douglass
photo: Yosemite Valley view from Taft Point