Hardeg Castle, Medieval castle in Hardegsen, Germany

Hardeg Castle consists of the Muthaus, a 35-metre-high residential tower of dark rough stone built in 1324, and a lower, longer wing with a white-rendered facade and red-tiled roof added in 1780. The Muthaus is considered the oldest fully surviving secular building in southern Lower Saxony. A stone wall and metal railings stand at the base.

The original noble family of Rosdorf built the castle but faced financial strain from major renovations and sold it in 1379 to Duke Otto of Brunswick. After being expelled from Göttingen the following year, Otto made the site his new seat of government.

The great ceremonial hall in the main tower now serves as a registry office, blending medieval architecture with modern civic ceremonies. Visitors experience how a historic structure continues to play an active role in the community's everyday life.

The castle is managed by a Cultural Project organization that reinvests all rental income toward maintaining the historic structures. Visitors should check ahead of time, as opening times and accessibility may vary depending on ongoing preservation work.

The Muthaus was saved from demolition around 1780 only because its massive walls made tearing it down too expensive; it had already served as a granary since 1682/83. Its roof was re-covered with clay pantiles after work began in 2020, and facade repairs to the roughly 700-year-old sandstone masonry are planned.