There's a shorter hike (2.0 mi round trip) to the Lookout, coming from the North, if you're pressed for time. Take the dirt road North from the Bandy Creek campground, at SECOND fork, bear right. There's a small parking area at the terminus. NP Ranger visitor center can give you the details.
Great caves along the river walk portion if you enter from Leatherwood. Kids will love the caves!
Vanessa R. on O & W Railroad Trail
I love O&W in the Autumn, its beautiful. Also, if you want a challenging hike, do the Devil's Den. This hike is mostly up hill, take your time to enjoy the views, and for safety...but its well worth it. It's part of the John Mur Trail.
Vanessa R. on Leatherwood Overlook
It was a beautiful, easy hike. This would also be an amazing view in the Fall.