Peer close to the inner face of the northern bank and a stone lintel is visible in the gap, the architectural signature of a souterrain beneath. These underground passages, typically stone-lined and roofed with large flat slabs, were built during the early medieval period, most commonly as places of refuge or storage attached to a settlement. What sets this one apart is quieter and stranger: sea shells have been found inside it.

The rath to which the souterrain belongs is a ringfort, the circular earthen enclosure that was the standard farmstead type in early medieval Ireland, roughly from the fifth to the twelfth centuries. Thousands survive across the country, though many are known only as cropmarks or damaged earthworks. The souterrain here sits close to the inner face of the northern bank, which is the usual arrangement; builders positioned these underground chambers to be accessible from within the protected interior of the settlement. The presence of sea shells inside is the detail that lingers. Shells turn up in archaeological contexts for various reasons, from diet to lime production to simple accumulation over time, but finding them in a souterrain, a typically dark and enclosed feature, raises quiet questions about how this particular underground space was used or what found its way into it over the centuries.