Liberty Reservoir was created by damming the North Branch of the Patapsco River, creating an approximately 3000 acre lake. The dam was completed in 1954. Over 9000 acres of land has been set aside to create a buffer zone around the reservoir. The lake and buffer area provide hiking trails, fishing, birdwatching, and herping opportunities. Wild Turkeys have also been reintroduced here and seem to be doing quite well. See the Maryland Department of Natural Resources website for information.
Soldier's Delight and also the Bare Hills (see the description for Lake Roland in North of Baltimore) are very interesting area geologically as well as biologically. I highly recommend reading the descriptions on the links below before visiting to help appreciate the unique features. These areas are called Serpentine Barrens for the green mineral Serpentine found here, and for the sparse vegetation. There are only four Serpentine Barrens in Maryland, two of these including the Nature Conservancy's Pilot Serpentine Barren, are not open to the public.
Managed by the National Park Service. This Frederick County park has camping and cabin rentals and many hiking trails. I have not been to Catoctin Mountain in years, but I do love the area. The forest here is composed of northern plants including black birch, hemlock, and sugar maple trees. Very colorful foliage in the fall and an excellent place to look for woodland wildflowers such as dwarf ginseng, bluets, and showy orchid in the spring. Adjacent to Cunningham Falls State Park.
More information and directions can be found at the National Park Service website. www.nps.gov/cato/