Like the directions say, this is an old canal towpath. It is flat, wide, and anti-challenging. The trail runs from Trenton to New Brunswick, offering over 70 miles of trail. This run however just goes from Bridge St. in Lambertville, NJ to Bridge St. in Stockton, NJ.
From Bridge St. Lambertville: Trail starts right off trail near Greene St. Consignment and Lambertville Station Pub. Follows D&R Canal on old towpath.
http://www.singletracks.com/item.php?c=1&i=3401