The trails are at the Beaverdam State Recreation Area at Falls Lake State Park. To get there, take Capital Blvd US1 North to Hwy 98 in Wake Forest. Take 98 west to NC 50 (Creedmoor Road) in north Raleigh. Turn right and you will cross Falls Lake. The entrance is a mile ahead on the right. Go through the gatehouse and follow the signs. $4 charge per car from Memorial Day to Labor Day. Free from Oct-Mar.
Review: This was an awesome trail that goes forever. I don't know about markets along the way like Chris Barber wrote about, so you might want to bring your own water and snacks. Easy parking right off the trail.
Review: This is a really cool trail that apparently extends for 26 miles. I didn't run a marathon out here but it sounds like you can. There are plenty of markers to show you along your way. It is singletrack and very scenic. Great summer run with ample shade. Also really fun with switchbacks, roots, and rocks for a technical run. This is a great place for avid trail runners.