Souterrains, which typically consist of one or more narrow corbelled or lintelled chambers connected by low crawl-ways, are found in their hundreds across Ireland. Their precise function is uncertain, though cold storage, refuge during raids, and ritual use have all been proposed at various sites. The one at Killonerry is registered as a monument, which tells us it exists and has been formally recognised, but very little else about it has been made publicly available.

The scarcity of detail here is itself worth noting. Many souterrains were built roughly between the seventh and twelfth centuries, often in association with ringforts, the enclosed farmsteads that were the dominant settlement type of early medieval Ireland. Killonerry, a townland in the Kilkenny countryside, would have been part of that broader agricultural and social landscape. Without specific excavation records or historical documentation in the available sources, the particular history of this souterrain, who built it, when it was constructed, and in what condition it survives, remains unrecorded in any accessible form.