Patapsco Valley State Park is sort of a hidden treasure amongst the outskirts of Baltimore City.  I would have never guessed it to be there.  On our way home from our search for a pumpkin for this year's fall season, we came across a sign for the State Park and decided to stop in since it wasn't too late.  Patapsco River runs right along or through the State Park so it was very scenic.  There are multiple hiking, biking and horseback riding trails (some of which you have to be brave enough to cross the swinging bridge) in which you can see remains of historic buildings like the old Grist Mill and Flour Mill.  You can also fish, archery hunt, canoe, camp (which consists of several different areas), or just go for a day trip and picnic at the parks.