It is a souterrain, a type of structure built during the early medieval period in Ireland, typically consisting of one or more dry-stone chambers connected by low crawlways and dug into the earth or cut into rock. Their precise function has long been debated, with theories ranging from cold storage for dairy produce to places of refuge during raids. Whatever its original purpose, the one at Cartron belongs to a tradition of subterranean construction found across Ireland, particularly in areas of early Christian-period settlement.

Beyond its classification and location, the specific details of this souterrain remain obscure. No excavation findings, no measurements, no associated finds, and no historical accounts drawn from the site are currently available through public channels. It exists on the map as a confirmed monument, a dot marking something real and old beneath the Mayo ground, but the particulars of its construction and any objects recovered from or near it have not been made accessible. This kind of gap is not unusual for souterrains in the west of Ireland, many of which were noted by early fieldworkers but never subjected to formal excavation or detailed survey publication.