These structures, whose name derives from the French for "underground passage", were typically associated with ringforts or settlement sites, and served variously as places of refuge, storage for perishables, or concealed escape routes. Hundreds survive across the country, though many remain unexcavated and poorly documented, their full extent unknown even to those who farm the ground above them.

The souterrain at Cullin is one such site. Beyond its location in this quiet Mayo townland, the specifics of its construction, dimensions, and associated monuments remain, for now, largely unrecorded in the publicly available literature. What can be said is that Mayo has yielded a significant number of early medieval underground structures, often linked to the dense scatter of ringforts that once organised the rural landscape of early Christian Ireland. Whether the Cullin example is a simple single-chamber construction or a more elaborate multi-passage arrangement is the kind of detail that awaits closer investigation.