The region comprises the northwestern part of the Harz mountains. The Harz National Park is part of this district. The highest peak is the Wurmberg (971 m) near Braunlage, also being the highest elevation of Lower Saxony. Above the small town of Altenau there is the source of the Oker river, which runs through the picturesque Oker valley to leave the Harz at Vienenburg.