Love it or despise it, High Rock--in all of its gratuitous, graffiti-covered glory--is a Maryland must-see.
Start your hike where the AT crosses Raven Rock Road (Maryland Route 491). This crossing is well-marked from both sides by large, yellow signs and blazed stakes. You will need to park on the side of the road, but the shoulder is wide and can accommodate a crowd.
The first half mile or so of this hike is hard; you'll be climbing more than a thousand feet up uneven stone steps and switchbacks. Luckily, it's immediately scenic as you meander through Raven Rock Hollow, a large outcropping of boulders overlooking South Mountain's eastern ridge.
About 1 mile in, you can opt for a side trip to the exceedingly cool Devil's Racecourse or stay on the trail for about 1.7 miles to reach High Rock--the highest point in the Free State. Sadly, it's covered in graffiti, but the views are still unspoiled.
Note that there is a road up to and parking lot next to High Rock. You will probably not be alone up there. But you can feel satisfied in knowing you used your feet to make it to the top, and not your gas pedal.
Retrace your steps for an easy, all-downhill return to the car.