The construction of Fridau was initiated in 1872 by the village doctor Dr. J. Sidler and opened in 1874 as a lung sanatorium, later run as a health resort. In 1921, the canton of Solothurn acquired the institution and ran a psychiatric clinic here as an outstation of Rosegg. The ward was closed in 2008.
The facility is located 660 m above sea level, at the southern foot of the Jura, in the north of the municipality of Egerkingen, outside the settlement area on the connecting path over the first Jura chain in the direction of Langenbruck.
