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!
The principal routes leading northwest into Potomac from D.C. are River Rd and the Clara Barton Pkwy (which runs parallel to the smaller MacArthur Blvd). From Bethesda, take either River Rd or Democracy Blvd (from Old Georgetown Rd). From Rockville, the main route is MD-189 Great Falls Rd. From Virginia, bridges across the Potomac River are very few—you will almost certainly need to take the Beltway to the Clara Barton Pkwy, River Rd, or Democracy Blvd exits (for Democracy Blvd, head towards I-270 instead of continuing on I-495 at the split).
Potomac is not very public transport friendly, but there are a couple bus routes worth noting. The T2 Metrobus  runs every half hour throughout the day along River Rd and Falls Rd between the Friendship Heights and Rockville Metro stations. Ride on Bus #29 goes from the Bethesda and Friendship Heights Metro stations to Glen Echo Park (see below).
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.