Not really a high concentration here, but the cache "The Silent City" GCQYTG, is a couple of blocks from the Armory/Stadium metro stop. It's a multi-cache, took me less than two hours. Had a really outstanding and educational experience. Bring some Navy related swag, or gold&blue, if you have it.
I'd stopped here, after doing some caches at Arlington Cemetery, which does have several virtuals, which is also very close to a metro stop.
Good luck, VT