The cashel, a type of early medieval stone enclosure, contains within its bounds a souterrain, one of those narrow underground stone-lined tunnels built by early Irish communities for storage, refuge, or both. What makes this particular example quietly compelling is not what can be seen, but what cannot. By the time an inspection was carried out in 1999, no clear traces of the structure remained at the surface, leaving only a low grassy hummock in the western interior of the cashel as a tentative indicator that something archaeological lies beneath.

The souterrain appears on both the 1897 Ordnance Survey 25-inch plan and the 1920 edition of the 6-inch map, marked with a small rectangle and labelled simply as 'Cave', which was the common cartographic shorthand of the period for such features. Thomas Johnson Westropp, the prolific Clare antiquary, described it in 1896 as oriented northwest to southeast and situated in the northwest interior of the cashel, roughly 3.66 metres from the enclosing wall. Westropp was a meticulous observer, and his note is now the most detailed first-hand account available, since the structure has effectively withdrawn from view in the century since he recorded it. Whether it collapsed, silted up, or simply sank further into the earth is not known.