Authorized in 1978, the Lowell National Historical Park is located on 141 acres in the heart of downtown Lowell. The park, one of 388 under the auspices of the National Park Service, preserves and interprets the history of the American Industrial Revolution. The park features historic cotton textile mills, 5.6 miles of power canals, operating gatehouses, worker housing, and 19th-century commercial buildings. The Boott Cotton Mills Museum, "mill girl" boardinghouses, and the Suffolk Mill Turbine Exhibit are also here. The trolley, of early 1900s vintage, is available for transportation within the park. Lowell National Historical Park hosts the Lowell Folk Festival, the largest free folk festival in the United States, at the end of July. The festival presents three days of traditional music, dance, craft demonstrations, hands-on-activities, street parades, and ethnic foods on six outdoor stages. Lowell National Historical Park is affiliated with the Smithsonian Institution, and can therefore temporarily borrow objects from the Smithsonian's collections, including those of the National Museum of American History and the Center for Folklife and Cultural Heritage.