I've been doing small-group cultural travel in the Irish Gaeltachts (Irish-speaking regions) for a long time. And when I'm not with a group I'm rambling around the countryside looking for sites and just plaining enjoying the place. As a result of twenty-some years of that I have become intimately familiar with an area that is rich with archeological and historical treasures.
Among my favorite sites is one of the many that tourists will never see. From one little road (bohareen) you turn off on another, and then finally yet another after passing through a tiny three or four house village, or baile. Then you hike across a farmer's field, watching out for his bull as you go. Finally you come to a slightly raised embankment which, if you climb it, you can see is part of a more or less circular enclosure. You have found a very early monastic settlement. Against one bank of the enclosure, hidden among bracken and wild rose bushes, is a small stone holy water fount. Above it sits a vertical cross-inscribed stone. (Local legend has it the roses cannot be transplanted, as they will grow nowhere else but this little enclosure.)
The site is clearly pre-Viking as it is very close to the sea. After 850AD when the Northmen began their raids along the western Irish coast no one would have built so close to a landing place. Local legend has it that the site antedates Patrick, and is surely one of the earliest Christian sites I have ever visited, perhaps dating to before 400AD.
I've included a picture with the inscribed cross emphasized so it may be located by the viewer.