Located 25 miles south of Gaylord, Hartwick Pines State Park encompasses nearly 10,000 acres, including 49 acres of old growth pines. One of the largest state parks in the Lower Peninsula, it's also one of the most beautiful. Within it lie three mountain biking trails. Developed from old logging roads, access to the single-track trails is from the park's Michigan Forest Visitor Center. The 3.5-mile Aspen Trail is rated easy, while the more hilly 5.2-mile Deer Run Trail and 7.5-mile Weary Legs Trail are rated moderately difficult. A Michigan Recreation Passport is required for park entry and can be purchased for a nominal fee at park offices.