What remains is enough to read the craft of whoever built it: dry-laid rubble walls, a gently curving line running roughly north to south, and at the southern end, the original rounded wall still intact, as the builders left it.

The structure is a souterrain, a type of stone-lined underground passage or chamber found across early medieval Ireland, typically associated with nearby settlement sites. They were used variously for storage, refuge, or both, and are almost always found in close relation to above-ground enclosures. This one lies ten metres inside the western wall of Corwillick cashel, a stone-walled circular enclosure of the kind that served as a defended farmstead during the early Christian period. The two were almost certainly built as part of the same settlement. The roofing slabs are limestone, rectangular and substantial, the largest measuring roughly 1.8 metres by 1.5 metres, laid flat across the passage. The northern end is blocked with compacted earth, cutting off whatever portion of the souterrain may extend beyond the visible five-metre stretch. Whether that remainder collapsed or was deliberately sealed is not known.

The site is on private land within the broader cashel enclosure, and the souterrain itself can only be entered where gaps in the lintels allow, with a crawl space of just over a metre in depth. The blocked northern end means there is no through-passage, and the experience is essentially that of peering into a narrow, curving corridor that disappears into darkness and earth.