It was found during ploughing, noted by locals, and then covered back over, leaving no visible trace at the surface. That quiet erasure is its defining quality.

A souterrain is an underground passage or chamber, typically lined and roofed with stone, built during the early medieval period in Ireland as a place of storage, refuge, or both. The example at Doire Mhór Thiar came to light at some unspecified point in the past, the discovery recorded only through local information rather than formal excavation. When it was briefly exposed, the roof was found to consist of large stone flags sitting no more than half a metre below the surface, and the passage appeared to run at least twelve metres westward from its opening. That modest depth and the scale of the flagging are consistent with typical souterrain construction across Ireland. The site was subsequently covered over again, and no surface evidence survives to indicate where it lies.