The caves of the Hohlaub are shafts or fractures becoming too narrow, at best at -200m, much more often at about -20m. All? No, because one irreductible cave has resisted to the gravity. It has a long gallery with a typical phreatical genesis. This brings a new vision of the mountain and allows to sketch some hypotheses. The discovery has already led to the longest cave of the mountain and shown noteworthy neo-tectonics.