A souterrain, typically a stone-lined tunnel or chamber built during the early medieval period and associated with nearby settlements, is said to run beneath what was once a rath, a roughly circular earthwork enclosure used as a farmstead or homestead. The rath itself has been levelled over time, its banks long since flattened by farming or neglect. What remains visible is not the passage itself but a shallow depression in the southern half of the interior, a subsidence in the ground partly filled with a large stone. It is the kind of detail that might pass unnoticed, but it is precisely this sort of surface anomaly that can point to a collapsed or silted-up underground structure below.

The association between souterrains and raths is well established in the Irish archaeological record. These underground features were commonly constructed during the early medieval period, roughly between the seventh and twelfth centuries, and served various purposes including storage, refuge, and ventilation for adjoining structures. Their presence is often only known through local oral tradition, particularly in cases where the above-ground earthworks have been substantially disturbed or removed. At Shanvally, the rath itself, recorded separately, provided the original context for the souterrain; without it, the slight hollow in the ground would give little away. The large stone partially filling the depression may be the remnant of a lintel or roof slab, suggesting that whatever lies beneath was once deliberately constructed rather than simply a natural feature of the land.