From the guide
Bull Pen is as much rapid as waterfall. While not the most dramatic falls in the area, this is a great place to hang out for a while and explore the Chattooga River Trail. Also, the potholes in the rock are amazing and worth the visit.
From Cashiers, drive south on Hwy. 107 for about 7 miles until Bull Pen Road (one of the few turns off of Hwy. 107), and turn right. (If you see a stone processing facility on the left, you’ve just passed the turn.) Follow Bull Pen Road, which quickly turns to gravel for another 5 to 6 miles until you reach a bridge. Cross and park on the right. Bull Pen is right below and upriver from the bridge. There is a trail that leads ahead from the parking area upriver and a trail down to the rocks by Bull Pen across the bridge and to the right, though this trail is a fairly steep and technical way to reach the river.
All of the upper Chattooga is worth seeing, and Bull Pen is a good starting point. Another good hike here would start at the trailhead on Whiteside Cove Road, follow the Chattooga River Trail (Hiking) downstream and end here, at the Bull Pen bridge (this would require a buddy with a car, of course and a bit of planning).