Located in wonderful Waterford Michigan is a very nice trail by Pontiac Lake.
This was always a challenge for me when I was younger, and it still is now! The full suspension helps though.
Its got some nice climbs and lots of roots and rocks to roll over or avoid, your choice! The trail is well marked and is about a 13 mile loop.
These trails are excellently maintained by a biking organization known as CRAMBA. They also work on other trails in the area.