That uncertainty is precisely the point. The field is known locally as the 'religín', a diminutive form of the Irish word for a small burial ground or sacred enclosure, which hints that this patch of ground carried some significance long before anyone thought to fill it in. Today there is nothing to see at the surface, no depression, no hollow, no trace of an opening. The cave has been, in the most thorough sense, erased.

The 1842 Ordnance Survey six-inch map, one of the most detailed cartographic records made of rural Ireland in the nineteenth century, marks the feature plainly as 'Cave', which suggests it was open, known, and considered worth recording at that time. Local tradition holds that it was infilled sometime during the 1850s, and that it ran in a north to south direction. Why it was filled is not recorded. The site sits on the northern side of a modern lane, just below the crest of a hill that looks westward over the sea, and that position, elevated, exposed, overlooking water, is the kind of geography that tends to accumulate significance across centuries. Whether the cave was natural or modified, and whether the name 'religín' attached to the field reflects any actual use of the site for burial or ritual, remains an open question.

What survives, then, is essentially a cartographic ghost and a piece of oral memory, the map name, the directional detail, the decade of infilling, all preserved at one remove from the thing itself. The cave at Reen is a reminder that the Irish landscape contains a great deal that was once known, then closed over, and is now traceable only in old place names and older maps.