I think these are structures from the Southern Dinaric Karst System, the main geological structure and something quite common in that area. Karst comes from the croatian word <i>krš</i> and means stony dour soil. Most of your objects seems to be calcitic. The original sediments of the area, mostly limestone, was dissolved and finaly precipitated in structures like the ones you presented us here. So No, these are not fossil but Yes, these structures are quite interessting. Btw: That mountain is nice for skiing and was host for the the alpine competitions of the Olympic Winter Games of 1984. Very nice area!!
Best regards from snowy Germany 😉