This is one of Wisconsin’s Rails to trails gravel trails. It starts on S. Rolling Meadows. There is about half a mile north of the parking lot on S. Rolling Meadows (a Park and Ride lot with some spots reserved for trail users) that is paved with a cool bridge over Highway 41, but everything south of that is gravel.
It’s mostly flat, like all rails to trails, but it’s a long trail one (35 miles between Fond du Lac and Juneau), and pleasant too. Most of it is shaded, you’ll cross some roads, go under others, cross streams on wooden trestle bridges, mostly in the first half of the trail. There is a gas station about six miles in, if you need anything, and not far from the finish line you can find another one.
About 13 miles in, you’ll come by the Horicon National Wildlife Refuge and you can do the three-mile auto loop to do some birding, or get off the bike and hike a bit if you want to combine activities. There is a connecting trail between the Wild Goose and the trails within the Horicon Wildlife Refuge.