When a bulldozer moved in to knock down an old house at Castlegar in County Galway, the machine inadvertently revealed something that had been sealed beneath the ground for centuries, a souterrain that nobody above ground knew was there.

Souterrains are dry-built underground passages or chambers, typically constructed during the early medieval period in Ireland, and generally thought to have served as places of refuge, cold storage, or both. This one was built using the drystone technique, meaning the walls were laid without mortar, relying entirely on the careful placement of stone for structural integrity. The chamber itself was modest in scale, roughly 2.2 metres long and 1 metre wide, oriented on a NNW to SSE axis. Once the discovery was recorded, the souterrain was sealed again. Today, a single roof lintel is the only physical trace that remains visible at the surface, a fragment of the structure that once covered the chamber from above.