my family recently relocated to the DC area, and through an interesting quirk, we have MLK day off but the daycare does not. so naturally, we'd like to spend a day to ourselves!

we've done the smithsonian, the monuments, and the zoo. does anyone have ideas that are metro-accessible and can be accomplished before 4pm (so we can get home in time to pick up the kids)?

we're pretty much open to anything in DC or montgomery county (esp. rockville or bethesda areas), but crossing into virginia, prince george, or baltimore is a stretch.

thanks!