You'll be headed south on 355, so you'll need to turn around, perhaps using a left turn onto a side street. South of the Beltway, Route 355 is called Wisconsin Avenue. Get off at Georgia Avenue northbound. Follow the signs to the Van Dorn station.
Parking is plentiful.
Take the train toward Shady Grove. In about a mile, take the Connecticut Avenue exit south. Go a few miles on Connecticut, past the Zoo on your left, next over a high bridge over the park, then look for the Washington Hilton Hotel on the left. Just past the hotel, take a right turn on to Florida Avenue. In a half a block or so, the Meetinghouse will appear on the right.