大阪府 (Ōsaka-fu, Osaka Prefecture) is actually more or less the city of Osaka. The third-largest city in Japan Osaka Bay, where the Yodo and Yamato rivers flow into the sea. However, the bay is separated from the sea by several islands. The prefecture has actually only a single underground site, which is an underground city, actually an underground shopping mall which connects other malls and department stores. The main area of the prefecture is lowland and was filled in, to build the city. The borders are mostly low mountain ranges which are sparsely populated and mostly designated as Natural Parks. 11% of the total land area of the prefecture has been designated as Natural Parks.