You may begin the fun with lunch at the Blue Moon Cafe in Shepherdstown, West Virginia, highly recommended with its large and varied menu, good food (and beer), sure to please most everyone (including babies and dogs) in a delightful, shaded outdoor setting with indoor seating, too.
After tasty treats, you may proceed through Shepherdstown and Shepherd University and head over the bridge atop the Potomac River into Maryland, home of the Ferry Hill Historical Park which is up the hill and immediately to your left. There you will find free bikes, helmets, and a National Park Service guide (if you're lucky, she'll be Cindy Brockman) to lead you along the street and down, down, down the path to the grassy green wonder of the Ohio and Chesapeake Canal Towpath.
You can walk, run (with a tire), or ride the trail in gaps, like we did, starting at the Ferry Hill Mansion and ending at the Antietam Aqueduct (about six miles round trip). The trail straddles the Sharpsburg/Antietam Battlefield, and is beautifully shaded which helps keep you cool.
The park is "trash free," meaning you take out what you bring in, and at the Ferry Hill Mansion, no bottled water is sold, so take your own container or buy one there.
Exercise, an outdoor setting, nature, fresh air, camaraderie with friends, tranquil scenes, history, butterflies, sunshine and Vitamin D, all things good for you and available at no charge at Ferry Hill.