Schaumburg Castle, Medieval château in Balduinstein, Germany.

Schaumburg Castle is a stone fortress that rises from an elevated position above Balduinstein and overlooks the Lahn valley below. The structure displays architectural elements from different periods, as it was expanded and modified over the course of several centuries.

A castle may have stood on the hill by around 915, when the area was named in a donation to Weilburg Abbey; the name Schowenburg appears in 1197 as the centre of a lordship holding Biebrich, Cramberg and Steinsberg. From 1850 to 1855 Archduke Stephan of Austria rebuilt it in neo-Gothic style to plans by Carl Boos. After a court case of more than twenty years, the House of Waldeck-Pyrmont was awarded the castle in 1888.

The blue cross in a golden field of the Schaumburg lordship was borne in an overlaid heart shield by the House of Westerburg, which took over the Cologne share in 1276 and expanded the castle from 1279. From 1557 the Leiningen-Westerburg-Schaumburg sideline resided here. Archduke Stephan of Austria, owner from 1847 to 1867, kept a painting gallery, a library, a coin and mineral collection and a small zoo.

The castle is visible from outside and offers good views of the landscape around Balduinstein. Visitors should expect steep pathways and uneven surfaces, as the fortress sits on a hillside.

The main tower of Schaumburg Castle is the zero point of the Soldner coordinate system for the former Duchy of Nassau, a surveying grid established in the 19th century. The castle archive, kept through the centuries, was bought by the state of Rhineland-Palatinate and is held in the Main State Archive in Koblenz.