The Trout Run Trail is a paved loop around the town and river valley of Decorah, Iowa. The path is super popular all year long, as it is open to runners, walkers, cyclists, skiers, and snowshoers. It also connects to the Freeport Trail for some bonus miles if that's your jam.
There are a number of different trailheads along this 11-mile path allowing you to start and stop wherever you like. The southern section of the loop is known for having the most wildlife-exposure, in case that is what you are looking for.