Silesia is along the Oder River, with the Sudeten Mountains extending across the southern border. The region contains many historical landmarks and UNESCO World Heritage Sites. It is also rich in mineral and natural resources, and includes several important industrial areas. The largest city and Lower Silesia's capital is Wrocław; the historic capital of Upper Silesia is Opole. The biggest metropolitan area is the Upper Silesian metropolitan area, the centre of which is Katowice. Parts of the Czech city of Ostrava and the German city of Görlitz are within Silesia's borders.