Between the Dutch city of Nijmegen and the (nearby) border of Germany lies the nature reserve Duivelsberg (Devil’s Mountain), characterized by high hills (the top has a height of almost 76 meters) and deep valleys, springs and streams. It is a surprising area with beautiful forests, but also meadows and fields. . The nature reserve covers about 125 hectares (310 acres) and is predominantly covered with deciduous trees, especially chestnut. It is managed by Staatsbosbeheer (Dutch Forestry Commission).

It is politically significant, however, because Duivelsberg is the only part of the Netherlands that was both annexed from Germany and retained after World War II. During the war there was heavy fighting on Duivelsberg during the operation “Market Garden”. After the war the nature reserve - among other small pieces of land along the Dutch-German border - became Dutch territory. In 1963 the Netherlands gave the annexed German territories back to Germany, except Duivelsberg.

The area was for long times a place of great military interest. There was a Roman fortification established 2000 years ago. On Duivelsberg stand two mottes (large earthen hills on which once stood wooden palisades with a tower). A motte is the primitive forerunner of the medieval castle. This particular motte is known by the name “Mergelp” and was probably constructed by count Balderik and his wife Adela around the year 1000.