Mi sono sempre chiesto, ora finalmente mi chiedo: cosa sono queste viti che a volte trovi nei massi/rocce?

Not all have same explanation. It can be remains of some structure (building, tower, mast…), anchor point for a measuring device (not likely in this case as those are often round and have red paint) or if it is close to water attachment points for attaching a boat (especially by the sea since the level has gone down a lot in relation to ground).

This case looks like remains of some old structure. Can’t say much more than that. I have found remains of weather stations on Baltic sea islands that never had human dwellings.