The Lauenburg is a ruined medieval castle in the East Harz in central Germany situated on an elevation southwest of the village of Stecklenberg (in the borough of Thale) in Harz district in the state of Saxony-Anhalt in the former German Democratic Republic (East Germany).

The construction of the two-part castle with its inner and outer wards (Vorburg and Hauptburg) probably took up to ten years.

The purpose of this impressive fortification with a total length of more than 350 metres was the protection of Quedlinburg and the nearby military roads.

The only structure in the entire fortification that has withstood the ravages of time and history relatively well is the keep of the outer ward.

The path climbs steeply past a children's play park up to the ruined castle of Stecklenburg.