Big M has lots of rolling hills and some tough sandy climbs. The inner loop can be a bit tricky to navigate because of the many crossing trails, but it is very well marked with maps at most of the intersections. There's lots of options to create you own track through the network of trails on the inner loop. The outer loop is easy to navigate and a lot of fun to just hammer through the rolling hills.
From Manistee take Caberfae Hwy/MI-55 E. Then take a right at Udell Hills Rd (south). After about 3.5 miles you'll see a sign for Big M. Turn right into the parking lot. There is a $5 day use fee per car.
http://www.singletracks.com/item.php?c=1&i=3543