Baltimore
Luray Caverns and museums (I even liked the car and carriage museum, which I hadn’t expected), garden maze,
Great Falls Tow Path - While there are hiking trails, the boardwalk out to the falls and the towpath are more for strolling. Watch where you step on the towpaths, though, because some people ride horses there.
Hillwood - the Marjorie Merriweather Post estate - gardens and house - she had an amazing collection of Russian imperial treasures
Maryland Renaissance festival - fun, but only portapotties instead of regular bathrooms