At Tooraneena in County Waterford, a field holds a long shallow depression that most walkers would pass without a second thought. What it actually marks is the collapsed roof of a souterrain, an underground stone-lined passage and chamber system built in early medieval Ireland, typically beneath or beside a rath, the circular earthwork enclosures that served as farmsteads for the period's rural population. Souterrains were used for storage, refuge, or both, and they were carefully constructed affairs, their walls built from dry-laid stone and their ceilings sealed with heavy flat lintels. Here, that ceiling has long since given way, leaving the structure legible only as a sunken corridor running broadly east to west across the ground.

The passage, which extended to around 22 metres in total, followed a Z-shaped course rather than a straight line, a design that would have made movement through it slow and difficult for anyone unfamiliar with its layout. At one of the angles, a small circular chamber roughly 3 metres in diameter was incorporated, tucked into the bend. The passage then continued westward to terminate in a considerably larger circular chamber, 6 metres across, now entirely collapsed. The souterrain sits in the north-western quadrant of an associated rath, the two features forming part of the same early medieval complex. Despite the collapse, some of the original lintels remain visible on the surface, along with traces of the stone-lined edges of the passage walls, small details that reward a careful look at what might otherwise seem like ordinary uneven ground.