Cunningham State Park is located in Frederick county Maryland in the Catoctin Mountain range. It is actually two separate state parks, Catoctin Falls park and Catoctin Mountain park, that are separated by Maryland route 77. The combined parks take up 10,000 acres.
The park is full of hiking trails, but most visitors come to swim in the reservoir or make merry by the waterfall. The waterfall isn't mind-blowingly impressive, but watching it does beat watching television.
One small claim to fame for Catoctin State park is that it contains Camp David. Don't try to find it though. If you do you will be escorted back to your car by marines who pop out of the woods like they teleported in from nowhere.