It is a souterrain, the term used for the underground stone-built passages and chambers that early medieval Irish communities constructed beneath or beside their settlements, most likely for storage, refuge, or both. This one is modest even by the standards of the type: a single rectangular room, its long axis running northwest to southeast, measuring roughly six feet by four feet, with rounded corners and a roof of flat stone lintels. The walls narrow as they rise, giving the chamber a slightly tapered profile that is characteristic of dry-stone construction techniques of the period.