Its entrance was blocked up some years ago, according to local memory, and above ground the only visible trace is a large limestone slab, roughly two metres by one metre, lying flat among a scatter of smaller boulders. Without that local knowledge, there would be nothing to suggest that anything unusual lies beneath.

A souterrain is an artificially constructed underground passage or chamber, typically associated with early medieval Ireland, and thought to have served as a place of refuge, storage, or concealment. The Graigue example was investigated in June 1932, when Office of Public Works records described a passage aligned roughly north to south, running 7.2 metres in that direction before curving eastward for a further 2.5 metres at the northern end. The interior was reasonably substantial, between 1.5 and 1.8 metres in height and up to 10.2 metres in width at points, suggesting a well-built structure. What makes it particularly interesting is the mixed construction: the south and west walls were formed by cutting directly into natural limestone bedrock, making use of what the geology already provided, while the remaining walls were finished with a combination of quarried stone faces and drystone walling. The site sat along a former trackway leading to a house that is now abandoned, a detail that gives the whole place a quality of accumulated disappearance, one layer of habitation fading over another.