These modest signs, easy to overlook entirely, are thought to mark the position of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically used for storage, refuge, or both. The clues are sparse: the two openings measure around 0.7 metres in diameter, sitting to the east of the fort's centre, while a flat stone roughly a metre long and half a metre wide lies nearby.

The ringfort in which the souterrain sits, recorded separately as site 8405, belongs to a class of monument that was extraordinarily common across early medieval Ireland. A ringfort is essentially a circular enclosure, defined by one or more earthen banks and ditches, that served as a farmstead or high-status residence roughly between the fifth and twelfth centuries. Souterrains were frequently constructed within them, dug into the ground and roofed with large stone lintels, sometimes running for several metres in a series of interconnected chambers. At Kippagh, the structure has not been excavated, and its full extent remains unknown. What survives above ground amounts to little more than those two holes and a single recumbent stone, the kind of evidence that archaeologists treat cautiously, using phrases like "may indicate position" rather than making firm claims about what lies below.