It may be nothing. It may also be the collapsed roof of a souterrain, an underground stone-lined passage typically built during the early medieval period for storage, refuge, or ventilation, and found across Ireland in association with ringforts and enclosed farmsteads. The uncertainty itself is the point: the hollow sits there without yielding a clear answer, and no structural features have emerged at the surface to confirm what, if anything, lies beneath.

The suggestion that a souterrain might exist here came from a personal communication attributed to Leo Morahan, and the possibility has been noted in connection with the surrounding rath, a circular earthwork enclosure of the kind that served as a defended farmstead from roughly the sixth to the twelfth century. Raths are common across the Irish landscape, but souterrains within them are not always easy to identify without excavation. A depression at ground level can indicate a roof collapse, but it can equally reflect natural settling or unrelated disturbance. At Falleighter, that ambiguity has not been resolved.