The Clear Creek Natural Surface trails are some fun, winding singletrack. There are no major hills along the way, and this is a great hidden gem right in the city of Coralville. These trails are unmarked so they don't get much use, but you'll enjoy the solitude anyway.
Park in the Clear Creek Trailhead off of Camp Cardinal Blvd., and start making your way toward the woods. You'll see the path leading into the trees, and this is the start of the loop trail.