The access hole, set roughly six metres from the outer foot of the enclosing bank, has been blocked up, and the souterrain it once led into now exists mainly as inference and subtle ground disturbance. A souterrain is a man-made underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, and thought to have served as a place of refuge, storage, or both. Here, the evidence above ground is fragmentary but legible to a careful eye.

The ringfort itself, known in Irish archaeology as a rath, a circular enclosure defined by an earthen bank and ditch, is the context that makes the souterrain intelligible. Such underground structures were commonly built beneath or immediately adjacent to raths, and their entrances were often deliberately narrow and awkward, designed to slow an intruder rather than welcome a visitor. At Ballyogan, within the north-east quadrant of the rath, a small circular stone-lined hollow roughly 1.5 metres in diameter sits at the edge of what appears to be a disturbed area, and this depression is likely the result of a section of the souterrain's roof having collapsed at some point. Extending south-east from this hollow, a line of stones traces the edge of a slight rise in the ground, suggesting the buried passage continues in that direction beneath the surface.

What remains visible today is subtle: a blocked hole, a hollow in the earth, a low ridge marked by stones. The site does not announce itself, and that is rather the point. These features ask for patience and some prior knowledge before they begin to make sense as the outline of something once carefully engineered and deliberately concealed.