also the landscape (at least in cork) is dotted with ringforts, which were built from the bronze age through to 1000 ad. they consisted of earthen walls enclosing a small settlement with farm animals. my understanding is that almost none of them have been archaeologically excavated. nowadays they are usually considered unlucky and avoided by people.
My Mother showed me a whole area with these rock constructions out near Dingle. They lookes like constructed cave entrances but didn’t seem t go very deep. You are right the locals stay away from these locations.