It is the kind of structure that can be walked over without any sense of what lies beneath, which is precisely what makes it worth pausing over.

Souterrains are underground chambers or passages built from drystone masonry, typically associated with early medieval ringforts and enclosures, and thought to have served as refuges, storage spaces, or both. The Ballygarraun example sits roughly 20 metres to the south of a large enclosure, and its chamber runs east to west for more than six metres, with a width of about 1.9 metres, large enough to crouch in but not to stand with any ease. Access at the eastern end is gained through a sloping hollow, with traces of drystone walling visible on either side of the approach, suggesting this was once a more formal entrance. A blocked air vent in the end wall hints at the practical thinking behind such structures; whoever used this passage needed air to breathe, which rather argues against the idea that souterrains were purely for storage. The site was noted by Knox and Redington in 1916, and examined again by Knox in 1918 and by Cody in 1989, so it has attracted some scholarly attention over the decades, even if it remains largely unknown outside specialist circles.