Greater Potomac is an exceptionally affluent and densely wooded area of Montgomery County, Maryland, home to some 80,000 people, among them many of the wealthy and powerful of the nation's capital, as well as a near endless quantity of doctors!
Glen Echo  is a remarkable little town created out of an antique turn of the twentieth century amusement park! The small suburban park  was in operation until 1960, and subsequently salvaged by the National Park Service in 1971, looking to turn it into an arts and educational center. The park itself is open... free, although activities often charge very reasonable fees.
Concerts, art exhibits, dramatic performances, puppet shows, ballroom dancing in the historic Spanish Ballroom, and a whole host of educational programs (mostly related to the arts) are in full force throughout the summer, when you can also avail yourself of the still-operating, 1921 antique carousel ($1). Check the park's website for event dates and available classes.
For the benefit of the hungry summer visitors (since there isn't anything else nearby), the Spanish Ballroom Cafe is open from the beginning of March through the end of October.
To get here by car, take the Clara Barton/Cabin John Pkwy exit west from the Beltway. Go 2.5 miles and take the MacArthur Blvd/Glen Echo exit (this is a left exit). Turn left onto MacArthur Blvd. For the park, go two blocks to Oxford Rd (just past the Glen Echo shopping center) and turn left into the parking lot. It's easy to arrive by public transport as well—the #29 Ride on Bus  runs a route every half hour between the Bethesda and Friendship Heights metro stations, with a stop in Glen Echo, running roughly every half hour M-Sa. On sundays, the bus runs only between Friendship Heights Metro and Glen Echo, with no stop in Bethesda.