Often referred to as the "lungs of Madrid", the 17-square-kilometer Casa de Campo park is a large expanse of greenery located west of the Río Manzanares. Although Madrid has more centrally located and appealing parks, Casa de Campo holds plenty of attractions and is visited by up to half a million people each weekend. A major factor in the park's popularity is the fact that it was opened to the public by the short-lived Republican government of the 1930s, when it had previously been reserved exclusively for royalty.