National Park Service is a bureau of the United States Department of the Interior. It manages more than 350 facilities, such as national parks, monuments, battlefields, military parks, historic sites, lakeshores, recreation areas, scenic rivers and trails. It also administers various components of the National Trails system. The bureau employs more than 20,000 professionals and over 140,000 volunteers. Located in Washington, D.C., the National Park Service is supported by an association that offers several programs and park-related retail items in their shops. The bureau has more than 600 concessioners at over 120 different park units that provide visitors with lodging, transportation, food, shops and other services.