If you are willing to hike unarmed, I highly recommend the Billygoat Trail in the Maryland section of Great Falls National Park.
Park near Old Angler's Inn, start hiking upstream on the C&O Canal Trail to the well marked trailhead. It's a loop trail, takes over an hour (or much more if you stop to gawk at some amazing scenery. Allow two hours).
The main section of the park, with boardwalks and crowds, has better views but it's not what I call hiking. See both.
Tagged because I also need to find some gun-friendly trails.
"I do not believe that the president loves America"--Rudy Giuliani