Not a cave, not a cellar, but a souterrain, the name given to the deliberate stone-lined tunnels that early medieval communities dug beneath their settlements. Their precise function is still debated, with cold storage, refuge, and ritual use all proposed at various points, and most sites probably served more than one purpose over their working life.

What makes this particular site quietly interesting is its context. The souterrain sits within what may be a rath, a circular earthen enclosure of the kind built in great numbers across Ireland during the early medieval period, roughly the fifth to twelfth centuries. Raths served as farmsteads for families of some local standing, and souterrains are frequently found within them, suggesting the two features were conceived together rather than one added long after the other. The earliest published notice of the Lisnacrilla passages comes from Samuel Lewis, who included a brief reference in his Topographical Dictionary of Ireland in 1837, describing them simply as "subterraneous passages". That passing phrase is almost all the historical record offers, which is itself telling: Lewis was thorough enough to note the passages existed, but they evidently attracted no great ceremony or local legend worth recording in detail.