state parks
Fort Frederick State Park
Fort Tonoloway State Park
Gathland State Park
Greenbrier State Park
South Mountain State Park
Washington Monument State Park
national parks
Antietam National Battlefield
Appalachian National Scenic Trail
Chesapeake and Ohio Canal National Historical Park
Harpers Ferry National Historical Park
other recreation
Crystal Grottoes, the only show caves in Maryland.
Sideling Hill man-made mountain pass on Interstate 68/U.S. Route 40 roughly 5 miles west of Hancock shows off 100 million years+ of rock formation with Information Center and walkways on the premises.
Stoney Creek Farm
Washington County Rural Heritage Museum (http://www.ruralheritagem...)
Most non-historic attractions are located in Hagerstown or its immediate suburbs.