Baltimore? I'd pick the Baltimore museum of art over the Walters. Maybe it's because I really like the impressionism gallery there. What about the aquarium, and walking around the shops along the inner harbor? Do you like checking out some interesting neighborhoods? Charles Village, Broadway near Fells Point, Charles St. south of downtown, etc.

DC? The list is endless. Go see the monuments, and the museums. Google to see what the Smithsonian museums are. They are all free, as is the zoo. In addition to the Smithsonians, the Holocaust museum and National Gallery of Art are also free, and both very worth it. The Newseum and Spy Museum are not free. Some people walk along the horizontal axis of the Mall and forget to head south. Make sure to leave some time to go South, to the TJ and FDR memorials. Also, the MLK Jr memorial is very new and worth checking out. It's between Lincoln and FDR.