A souterrain, to use the term borrowed from the French for "underground way", is an artificial tunnel or chamber built, usually in early medieval Ireland, from dry-stone walling and roofed with large lintels. They are found in their hundreds across the country, tucked beneath ringforts and early settlement sites, and their precise purposes remain debated: cold storage, refuge during raids, or simply a place to keep dairy produce cool through a Connacht summer. The one at Pollacurra is recorded as a monument, but almost nothing beyond that bare fact has made its way into the public domain.

Because the available documentation for this particular site is so thin, the specific details that would normally anchor an account, such as when it was first noted, who owned the land, what its dimensions are, or whether any finds were recovered nearby, simply cannot be supplied with any confidence. What can be said is that souterrains in the west of Ireland tend to cluster around early Christian period settlements, broadly the sixth to the twelfth centuries, and that Galway's landscape conceals a considerable number of them beneath pasture and bog that has never been fully excavated. Pollacurra itself is a small townland, and the presence of a recorded underground structure there hints at a settlement history that stretches well back before any written record of the place survives.