A cashel is a type of early medieval stone ringfort, its perimeter formed by a dry-stone wall rather than an earthen bank, and this one contains something older and more secretive inside it: a souterrain, the kind of underground passage or chamber, typically stone-lined and roofed with flat slabs, that appears at early Christian and Iron Age sites across Ireland. They were used variously for storage, refuge, and purposes that remain debated. What makes this particular example quietly curious is not just its construction but what was done to it in living memory.

The souterrain has two openings. One lies within the cashel's interior, enclosed by a low bank of rubble limestone measuring roughly three by four metres and no more than forty centimetres high, built up against the inside of the cashel wall. The other opening is outside the cashel wall entirely, six metres to the south-east. Both are blocked with limestone rubble. The two lintels on the inner side appear to be in their original positions, suggesting the basic structure of the passage is still largely intact beneath the fill. According to local information, the blocking was carried out around 1987, after the souterrain had been informally investigated, a word that covers a range of possibilities from careful examination to casual digging. Whatever happened, the decision afterwards was to seal it up rather than leave it open or pursue any formal excavation.