The Potawatomi Trail, in Pinckney State Recreation Area, is a 17.5 trail which is scenic, somewhat hilly and somewhat technical. It is open to mountain biking as well as hikers. Mountain bikers are encouraged to travel clockwise while hikers, counter clockwise. The trail does has several sub-routes where you can traverse shorter distances however the full trail is 17.5 miles.
The Potawatomi Trail has a Strava Segment (but the trail name is mis-spelled).
Note that Jim O'Keefe reports running the Potawatomi Trail in a speedy 1h56m20s on 4/14/1985, but we do not have any verification of this, and are not sure if the trail at that time was the same as today.