The Balm ruins lie in the area of the municipality of Balm bei Günsberg in the Canton of Solothurn at the foot of Balmfluh. It is that canton's only cave stronghold and one of the few in Switzerland.
The stronghold was built 20 meters high in a natural cave of about 20 meters wide and 6 meters deep, in the Jura Mountains.
The 2.4 meter thick outer wall was provided with two doorways and some narrow windows. The wet rock face was covered with a lining wall; and the rest was a simple two-story timber construction, which is shown evident by the presence of holes used to insert beams into. While being restored, the today-visible wall-openings were distorted from their original form.
At a later stage in the building of the stronghold, a fortified, inhabited house with an inside width of 3.5 meters and a length of 29 meters was erected in the forecourt. Presumably this was a defensive fortification of some farming complex.The entrance to the stone fortress stretched over a long, partly walled rise which is partly hewed from the rock. The connection between the forecourt and the fortress itself is still only incompletely reconstructed. The present day rise is of modern source, and only partly represents its original state.
Excavations from the years 1939 and 1941 indicate that the place had been used as a habitation since early times.