National Park Service employees and volunteers safeguard and maintain the United States' 392 national parks. About 275 million people visit these places each year. There are tens of thousands of acres of land, oceans, lakes and reservoirs; 68,000 archeological sites; 43,000 miles of shoreline; 27,000 historic structures and much more. The National Park Service is a bureau of the U.S. Department of the Interior and is led by a director nominated by the president and confirmed by the U.S. Senate. (Source: NPS / Photo: Flickr)