The structure in question is a souterrain, a type of man-made underground chamber or tunnel commonly associated with early medieval Irish settlements, typically used for storage, refuge, or both. The problem is that the earthwork it was reportedly built within has been ploughed or cleared away, and the souterrain, if it exists at all, has left no trace visible at the surface.

The souterrain was said to lie within a rath, a circular earthen enclosure of the kind built across Ireland during the early medieval period, roughly between the fifth and twelfth centuries, and used as a defended farmstead. The rath at Shanvally has since been levelled, its banks and ditches absorbed into the surrounding landscape. With the enclosing earthwork gone, any underground feature associated with it becomes almost impossible to locate without excavation. What survives is only the tradition itself, passed down locally as a memory of a cave that once was known, or at least believed, to be there.