Visit the lovely Winterthur, nestled in Delaware's beautiful Brandywine Valley approximately 1.5 hours Northeast of Baltimore.  It's the estate that USA Today says is one of America's "10 great places of historical proportions" and Martha Stewart says is "definitely worth the trip."  

Founded by Henry Francis du Pont, Winterthur (pronounced “winter-tour”) is the premier museum of American decorative arts, reflecting both early America and the du Pont family’s life there. Its 60-acre naturalistic garden is among the country’s best, and its research library serves scholars from around the world. You are invited to visit and explore this place of beauty, history, and learning.

http://www.winterthur.org 

And consider a trip to Longwood Gardens as well!