The Harlyberg hill (256m/840 ft) north of the town was the site of a castle built in 1203 by the Welf king Otto IV of Germany to threaten the trade route to Goslar, as its citizens supported his Hohenstaufen rival Duke Philip of Swabia. After Otto's death in 1218 the castle became a property of the Welf Dukes of Brunswick-Lüneburg and a thorn in the side of the Bishops of Hildesheim, while the garrisons of the castle were notorious for permanently robbing bypassing merchants. Therefore, Prince-bishop Siegfried II of Hildesheim declared war against Duke Henry I of Brunswick and in 1291 took and slighted the castle. Some moats are still visible today. A modern observation tower stands nearby.