Running south from the centre of a rath, a linear hollow measuring roughly fourteen metres long and just under four metres wide cuts toward a gap in the enclosure's perimeter. A spur branches westward from it, tracing a further eight metres just inside the bank. No stonework breaks the surface, and yet the geometry is deliberate enough to suggest that something was once here, or still is, beneath the grass.

A rath is a roughly circular earthwork enclosure, typically of early medieval date, used as a farmstead and settlement. Souterrains, the underground stone-lined passages sometimes found within or beside such enclosures, served various purposes, from food storage to possible refuge. They are usually identified by collapsed rooflines, exposed stonework, or the telltale subsidence of ground above a void. What makes this site at Corrinshigo unusual is the absence of any visible stone, leaving open the possibility that what appears to be a souterrain is something else entirely, perhaps a drainage feature, a field modification, or simply an unrelated earthwork. The drumlin landscape of Monaghan, shaped by glacial deposits into its characteristic rolling hills, is dense with such ambiguities, where ancient human activity and natural landform blur into one another and resist easy classification.