The ground gives nothing away: no depression, no hollow, no stonework breaking the surface. The only reason anyone knows of it at all is that, around 1954, the earth briefly gave way.

Souterrains are underground passages or chambers, typically earth-cut or stone-lined, built during the early medieval period in Ireland. Their precise function is still debated, though cold storage and refuge during times of danger are the most widely accepted explanations. The collapse at Lisnabrinny offered an unplanned glimpse of what lies below: a souterrain of possibly three chambers, cut directly into the earth rather than constructed from coursed stone. That momentary opening was apparently enough to establish the basic shape of what is there, but not enough to invite excavation or formal investigation. Since then, the surface has settled back, and there is once again no visible trace of anything beneath the field.