Directions via I-66.
I-66 all the way to Washington (inside the Beltway).
The last exit before going across the Potomac River is Rt. 110. This will take you past the Pentagon. Continue straight through under I-395 and into Crystal City.
Look for the National Airport exit on the right, and then it curves to the left over the road you just left. You'll see National Airport just ahead past a stop light.
Just after the stop light, exit to the right for "to I-395". This will put you on the GW Parkway North, taking you past the airport.
After you pass the airport, the entrance to Gravelly Point will be on your right. Park in the lot to be safe.
Gravelly Point is at the north end of the runway at National Airport on the river side (northbound side) of the GW Parkway.