The Potomac Heritage Trail is one of my favorites here in Sterling. It is just off of Cascades Parkway as you head towards Algonkian Park. Right before the park you will make a right hand turn into the Potomac Lakes Sportsplex.
Drive around the parking lot until you see the picnic pavilion, and park there. Just behind the pavilion you will see a trail. To the left is a huge playground, but to the right is where the trail begins. In about a mile you will come to a waterfall and a bridge. The trail is covered by a canopy of trees and is a great path to see all sorts of wild life.