Chapultepec, more commonly called the "Bosque de Chapultepec" (Chapultepec Forest) in Mexico City, one of the largest city parks in the Western Hemisphere, measuring in total just over 686 hectares (1,695 acres). Centered on a rock formation called Chapultepec Hill, one of the park's main functions is to be an ecological space in the vast megalopolis. It is considered the first and most important of Mexico City's "lungs", with trees that replenish oxygen to the Valley of Mexico.