Duncan Hollow is a 17 mile loop trail located near Woodstock, VA and is rated as difficult. The trail is primarily used for mountain biking and is accessible year-round.
The Duncan Hollow Trail is quite a monster - it is difficult, and certainly not for beginners, and even intermediate riders should beware of the difficulty presented by this trail. The trail can be ridden in either direction...I know this because we did it in the "wrong" direction and were able to complete it (with a significant amount of hike and bike).
The trail starts at the horse trail parking area on Camp Roosevelt Rd. We rode down the hill (30+ mph!!) to the intersection with FR274, then climbed FR274 to the Scothorn Gap Trail (~4.5 miles steady climb, 600' elevation gain). From there the trail was rideable for a few hundred yards (until shortly after crossing the Massanutten connector trail) before rising sharply (10% grade and more) along a loosely cobbled trail that defeated most of our best efforts to ride it. The loose cobbles on top of larger rocks made getting necessary traction extremely difficult. We spotted bear scat along this part of the trail.
After cresting the ridge at Scothorn Gap (make sure to look for the saddle pond), the trail continues to climb almost straight up the ridge to cross the Middle Mountain Ridge. The down trail is steep, treacherous and loose, but exciting and rideable. Hardtails, watch for flat rocks and cobbles that seem to be spaced exactly far enough to make control an iffy matter down the switchbacks.
Once you reach the trail along Duncan Hollow (turning NE), the going is better, with sections that are great singletrack. Still, we lost a chain and a tube along this section, but that is probably due to the fact that we could actually ride and gain significant speed along this section. Once you reach the Duncan Hollow Rd. (marked by a sign), the trail veers right, along and across the creek, back towards the trail parking area. This section is softer, and shows moderate signs of use from horses - It could be much worse in wetter weather.
As mentioned above, the trail can be ridden in the opposite direction (as evidenced from descriptions elsewhere) - that may make it easier, since the switchback climb on the east side of Middle Mountain seemed more do-able than climbing the West side of Waterfall Mountain along the Scothorn Trail. The ride down would be hard on body and bike, but is within reason.
The forest has been recently burned (intentionally) - north of the Scothorn Gap Trail, and west of the Duncan Hollow Trail. It makes for some stark views, and we saw little wildlife. We passed several hikers, and indications are that there are good views from some of the knobs up higher.
Bring plenty of water, as there is not easily potable water along the route.
Overall, the route is NOT one that I will highly recommend, but I might be convinced to try it in reverse on another occasion.