Wistfully whiling away time in Washington while wife works

We have done Lake Fairfax a few times. Much less $ than Cherry Hill. Plenty room between sites. Many very long sites. Inside a very large park with plenty of trails if that is of interest. Not far from the Dulles Air & Space Museum, which outdoes the one downtown many times over. Not near any major highways so no noise. Were it not for the Dulles air traffic, which is not much in the evening, you would think that you are miles away from any city.