You can also use the car to simplify your sightseeing closer to the Beltway— for that matter, inside the District— rather than dealing with taxis or buses to get to places like

• National Cathedral
• National Arboretum
• Great Falls + Clara Barton Parkway
• Hillwood Museum
• Wolf Trap (if there is a show you're interested in)

Farther afield, the Udvar-Hazy Center, Mt. Vernon/Collingwood and the Marine Corps Museum have been mentioned, and you can hit 4-5 B-list places instead of driving 3 hours to rush through 2 A-list places. There's Roaches Run if you like birds. The NRA museum if you like guns. Claude Moore Colonial Farm if you like living history. It's not the season for golf now, but of course you need a car to get to any decent golf course in the area.

A C-List might include stops at the Air Force Memorial, Brookside Gardens, the Kreeger museum, the National Women's History Museum, or along the C&O Canal.