This is one of the nicest loop hikes in Shenandoah National Park, going deep into the park's wilderness and involving a hike over a summit and along one of the park's prettiest streams. Any time of the year is nice for this hike; spring will feature wildflowers and potentially interesting stream crossings, summer will tempt hikers to cool off in the pools and cascades of Jeremys Run, fall will delight with colorful foliage, and winter brings the best trail views and the possibility of spectacular snow and ice formations along the stream.
Although this route is usually done as a day hike of 4.5-7.5 hours, it is also nice, perhaps nicer, as an overnighter.
The trailhead for Knob Mountain is at Milepost 24 of Skyline Drive in the park's North District. This is also where the Elkwallow facilities are located. Park in the picnic grounds at the furthest parking area from the drive. The trail begins here and is well marked.
You can follow this route as described or in reverse, but it is better followed as described so that the 1600' of elevation change over 2.4 miles between the summit and Jeremys Run is taken downhill.
Start from the trailhead (see Getting There) and hike 0.3 miles downhill to Jeremys Run Trail, where you turn left onto it. In 0.7 miles, turn right onto Knob Mountain Cutoff Trail, which leads steeply uphill for 0.6 miles to Knob Mountain Trail, at which point you turn left. It is now 3 miles to the summit, which is marked by a concrete post, as are all the trail instersections. The summit and the entire trail are wooded, but obstructed views east and west accompany the route on Knob Mountain. Winter is the best time to enjoy the views since the trees will be mostly bare.
After 2.6 more miles, the trail crosses Jeremys Run and reaches the trail of the same name. The final descent to Jeremys Run is steep-- dropping 1600' from the summit of Knob Mountain to the stream-- but some nice views compensate.
Turn left and follow Jeremys Run upstream for 5.6 miles until you reach the AT and the spur trail that you took to get started. Follow them for 0.3 miles back to the trailhead.
The Jeremys Run Trail involves 16 stream crossings. Much of the time, these crossings are ankle-deep or can be rock-hopped, but periods of heavy rain or snowmelt can make the crossings more difficult, even dangerous. Jeremys Run itself is a delightful series of pools, rapids, and small cascades. There are no major waterfalls on the stream, but it is beautiful nonetheless.
In all, this 12.9-mile hike involves about 2000' of elevation gain, more than half of it along the gentle-to-moderate grade up Jeremys Run.
I recommend waterproof boots for ankle protection on the steeper grades and for comfortable, safe stream crossings. Trekking poles are advisable to help with stream crossings.