A souterrain is an underground stone-lined passage or chamber, typically associated with Early Medieval ringforts and used variously for storage, refuge, or concealment. What makes this one quietly arresting is not anything visible above ground, but a single line in the 1842 Ordnance Survey Name Books describing a cave "with rooms" inside the ringfort here. That phrase, modest and matter-of-fact, suggests a structure of some complexity, perhaps a series of connected chambers rather than a simple tunnel. Today there is no surface trace of any of it.

The ringfort itself, recorded separately, forms the broader context. Ringforts, which are enclosed farmstead sites usually dating from roughly the sixth to the twelfth centuries, frequently contained souterrains as functional annexes to domestic life. The 1842 Name Books were compiled by Ordnance Survey officers gathering local placename and topographical information across Ireland, and their note about a cave with rooms at Knockrour is the earliest written record of whatever lies below. Whether the structure was already largely buried by that point, or whether it has since been obscured by agriculture or collapse, the current situation is the same: nothing to see at the surface, and a centuries-old underground space whose precise condition is unknown.