Kettle Moraine State Forest—Southern Unit: Nordic Ski Trails Professional Review and Guide
"If you are looking for a long trek with a bit of a workout, this may be it. The loop listed as most difficult surely earns its label. The terrain of Kettle Moraine is frequently marked by repeated steep ascents and declines—short distances, to be fair, but at times coming like waves. But the forest, the bluff-top views, old oaks, pine plantation and sections of prairie are fantastic, and options for shorter routes or bypasses for the hardest sections are numerous.
While you are not likely to encounter a lot of people, those here are often runners since the distances are long and you can pick and choose when it comes to the challenge of the terrain. The described hike takes the longest of the routes, the Blue Trail, but throughout the system, other colored trails are embedded within the larger loops and off er places to either shave off a couple of miles, skip a series of steep hills, or just give you a different part of the park to look at from the last time you were here."