The uncertainty is almost the entire story. A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts, and used variously for storage, refuge, or ventilation of dwellings above. At Knockrour, there is no visible surface trace of one. There is only a second-hand remark, committed to paper in 1939, that a local man named Mr. O'Leary believed a cave existed within the fort.

The note itself comes from P. J. Hartnett, writing in 1939, and it is a small but telling example of how archaeological knowledge was assembled in Ireland during that period, often through conversation with farmers, landowners, and local people who carried an unwritten awareness of what lay in the fields around them. O'Leary's cave may be a genuine souterrain, the kind of structure that turns up regularly in ringforts across Munster. It may be a natural hollow, a collapsed feature, or a memory of something once more visible that has since disappeared entirely under the ground. The ringfort itself, recorded separately, provides the context; souterrains are almost never freestanding, and their presence within a defended enclosure would be entirely consistent with early medieval practice in this part of Cork.