Hardenstein Castle, Medieval castle ruins near Herbede, Germany

Hardenstein Castle is a ruined fortified manor, or Festes Haus, on the south bank of the Ruhr between Herbede and Witten. Its south side was extended in 1430/40 with two flanking towers and a shield wall; a stretch of the main castle's inner wall collapsed in March 2010 and was restored by 2012. The site lies within the Hardenstein nature reserve, with the Muttental mining trail starting behind the southern wall.

Heinrich II von Hardenberg settled on the south bank of the Ruhr between Herbede and Witten in 1354, after selling the lordship of Hardenberg to Count Gerhard I of Jülich-Berg; the moated house was built between 1345 and 1354. His descendants called themselves von Hardenstein. In 1439 the castle passed by marriage to Robert Stael von Holstein, and around 1430/40 the south side gained two flanking towers and a shield wall. It was still inhabited in the 16th century and decayed only after being abandoned in the 18th century.

The castle is connected to local legends about a dwarf king who supposedly lived within its walls according to tradition. These stories have been preserved in regional memory for centuries and continue to shape how people perceive the ruins.

The ruin stands on the south bank of the Ruhr at Hardensteiner Weg in Witten-Herbede, reached on foot from the Muttental mining trail that begins behind the southern wall. The Ruhrtalbahn track now separates the site from the river, and the former Ruine Hardenstein stop has not been served since summer 2019. Since April 2006 the Ruhrtalfähre Hardenstein, the only ferry on the Ruhr, crosses to the Herbede lock; the excursion boat MS Schwalbe II uses the same landing. Parts of the walls collapsed in March 2010; restoration finished in 2012 and the ruin is walkable again.

According to a record from 1850, a dwarf king named Goldemar reportedly brought prosperity to the castle for three years. That period ended when someone attempted to uncover the secrets of this mysterious figure.