The university is organized into eleven principal academic units—ten faculties and the Radcliffe Institute for Advanced Study—with campuses throughout the Boston metropolitan area:[22] its 209-acre (85 ha) main campus is centered on Harvard Yard in Cambridge, approximately 3 miles (5 km) northwest of Boston; the business school and athletics facilities, including Harvard Stadium, are located across the Charles River in the Allston neighborhood of Boston; and the medical, dental, and public health schools are in the Longwood Medical Area.[23] Harvard's endowment is worth $40.9 billion, making it the largest of any academic institution.[4] Harvard is a large, highly residential research university.[4] The nominal cost of attendance is high, but the university's large endowment allows it to offer generous financial aid packages.[5] The Harvard Library is the world's largest academic and private library system, comprising 79 individual libraries holding over 18 million items.[26][7][28]