At some point in the past, the entrance was open and people could climb down into it. By 2001, that opening had disappeared entirely, swallowed up beneath dense overgrowth covering parts of the earthwork above.

A rath, to give the briefest explanation, is a circular enclosure defined by an earthen bank and ditch, the most common type of early medieval farmstead in Ireland. They were built and occupied roughly between the sixth and twelfth centuries, and hundreds survive across Cork alone in varying states of preservation. Souterrains are frequently found within them, constructed from dry-laid stone and often running for several metres underground. The one at Bawnlahan is known only through local information passed down over time, and the failure to relocate its entrance in 2001 says something about how quickly vegetation can reclaim even a known feature on a known site.