Harmony Hall, located in Fort Washington, Maryland, is managed by the United States National Park Service as part of the National Capital Parks-East system. It has been a National Park Service site since 1966. Harmony Hall is a 2+1⁄2-story Georgian country house built of red brick during the eighteenth century. It is surrounded by 65 acres of land o…Harmony Hall, located in Fort Washington, Maryland, is managed by the United States National Park Service as part of the National Capital Parks-East system. It has been a National Park Service site since 1966. Harmony Hall is a 2+1⁄2-story Georgian country house built of red brick during the eighteenth century. It is surrounded by 65 acres of land on Broad Creek, a Potomac River tributary.