Desenberg, Shield volcano and inselberg in North Rhine-Westphalia, Germany.

Desenberg is a cone-shaped basalt hill in North Rhine-Westphalia that rises sharply from the flat Warburg landscape and is topped with medieval castle ruins. The terrain features steep slopes that lead to a more level summit area where visitors can find the ruins and overlook the surrounding plains.

Desenberg Castle came into the possession of the von Spiegel family around 1250; in the 14th century the family split into the lines Spiegel zum Desenberg and Spiegel zu Peckelsheim. By the mid-16th century the Spiegels had left the hill for nearby knightly seats at Bühne, Rothenburg, Klingenburg, Übelngönne and Dalheim. The hill and the castle ruin remain in the hands of the Counts of Spiegel zum Desenberg.

The noble family von Spiegel took its name and three-mirror coat of arms from the legend of the Spiegelritter, a Saxon who slew a dragon on the hill by frightening it with the reflection in his shield. The family held Desenberg from around 1250; the castle ruins and hill remain in the possession of the Counts of Spiegel zum Desenberg.

The climb follows marked trails that start from different points in the surrounding area and offer varying difficulty levels. Those seeking the best views should go on clear days, as fog and rain greatly limit the long-distance views across the plains.

The hill is a textbook example of a volcanic pipe, or Schlotstiel, exposed by erosion: a basalt vein hardened inside a vent and the softer Keuper claystone around it wore away. The rock, a glass-rich alkali basalt called limburgite, carries xenoliths of mantle peridotite known as olivine bombs.