Blankenburg Castle with castle barn, Medieval castle complex in Zweisimmen, Switzerland

Blankenburg Castle is an L-shaped complex in Zweisimmen made of a two-story corps de logis and a single-story side wing that encloses a raised courtyard. South of the building lies a large terraced garden, and the former horse barn still belongs to the estate. The double covered staircase on the front echoes the staircase of Bern's town hall.

Blankenburg Castle was first mentioned in 1329, when it belonged to the Freiherren von Weissenburg. In 1378 the Lord of Düdingen sold it to Fribourg, and after the Battle of Sempach in 1386 Bern took over the Simmen valley and installed its bailiff at the castle. A fire in 1767 destroyed most of the medieval building; Niklaus Hebler rebuilt it between 1768 and 1770 on the old foundations. It remained the seat of the Bernese bailiff and later the district administrator until 2012.

The double covered staircase on the front of the building is a deliberate reference to the staircase of Bern's Town Hall, a sign that this was official, government architecture rather than a private residence. The building was commissioned as the seat of the Kastlan, the Bernese official governing the upper Simmen valley.

The property now functions as a meeting and reception center with restaurant facilities, having been converted by a community group from 2012 onward. Visitors should check opening hours and available offerings in advance to ensure their preferred activities are available.

In 1919 the prison cells at Blankenburg held Robert Grimm, the Bernese politician and leader of the 1918 general strike, which brought the castle national attention. Inmates were still housed in those cells until 1984, long after the building had become the seat of the OberSimmental governor.