The Loop is the central business district or downtown of Chicago, one of the city's designated community areas. The Loop is home to Chicago's commercial core, City Hall, and the seat of Cook County. In the late nineteenth century, cable car turnarounds and prominent elevated railway encircled the area, giving the Loop its name. The community area is bordered on the north and west by the Chicago River, on the east by Lake Michigan, and on the south by Roosevelt Road, although the commercial core has expanded into adjacent community areas. The Loop is home to 500 acre Grant Park; State Street, which hosts a historic shopping district; the Art Institute of Chicago; numerous theaters; and various subway and elevated rapid transit stations. Other institutions in the Loop include the Willis Tower, once the tallest building in the world, the Chicago Symphony Orchestra, the Lyric Opera of Chicago, the Goodman Theatre, the Joffrey Ballet, the central public Harold Washington Library, and the Chicago Cultural Center.