I'll hopefully soon be in that area as well. I'm heading to New York very soon for a family visit + wedding and plan on attending a workshop near Baltimore. I really hope to visit National Aquarium and Maryland Zoo and also want to try to squeeze in a revisit to National Zoo for the new bird house. If I end up in DC I might visit Glen Echo Aquarium just outside. Nothing rare there as far as I can tell but I like visiting small local places and interacting with staff. There's also the Calvert Marine Museum which also has a small aquarium, if you're interested in nautical history that might be a good place to visit.