Not to seal it, not quite to fortify it, but apparently to divide it, to create something that functions, at least in form, like a room. That detail is easy to walk past without registering how odd it is: drystone construction, the kind used for field boundaries and ringforts across Ireland, carefully fitted into a fossil cave passage no more than two and a half metres wide and one and a half metres high.

The cave sits about 280 metres north-west of Cahercommaun, a well-known triple-walled stone cashel, a type of early medieval circular enclosure, perched dramatically on a cliff edge in County Clare. The cave itself consists of two short, open-ended fossil passages, meaning passages formed by ancient water flow that dried out long before any human arrived, oriented roughly north to south and stretching a combined fifteen metres in length. The southern passage is where the human element becomes most legible. Drystone walls were built at both its ends, with the northern wall tucked just beneath the overhanging roof and the southern wall set back roughly a metre from the cave mouth. The effect, as far as can be determined, was to enclose a chamber within the passage. A pit cut into the cave floor adds another layer of interest: it revealed a shallow upper deposit of silty organic material resting on a sterile grey layer below, a stratigraphy that hints at use and perhaps at the deliberate deposition of material, though what that material was and when it was placed there remains unclear. The nearby Glencurran Cave, about 570 metres to the south-west, is itself a site of significant prehistoric finds, which places this modest walled passage within a wider landscape where caves clearly held meaning for the people who moved through it.