A farmer's plough broke into it around 1925, and what emerged from local memory was a picture of a souterrain, the name given to the dry-stone underground galleries that were built beneath and around ringforts throughout Ireland, likely used for cool storage, refuge, or both. The passage at Walshestown, by all accounts, had stone-lined walls and a lintelled roof, meaning flat capstones laid across the top rather than a corbelled or vaulted ceiling, a relatively common construction in Munster souterrains.

The detail we have comes from P. J. Hartnett, who recorded it in 1939, having been told about the chamber by people in the area. His account places the souterrain in the north-western quadrant of a ringfort, a circular enclosed farmstead of the kind that dots the Irish countryside in the thousands, running from near the fort's northern entrance in a south-westerly direction. Ringforts were the dominant settlement type in Early Medieval Ireland, their banks and ditches marking out domestic space rather than purely defensive ground, and souterrains were a fairly standard feature of better-appointed examples. At Walshestown, the precise line of the passage has never been formally excavated or mapped, and its full extent remains unknown. The only physical hint of its continued presence is a series of hollows in the south-western quadrant of the fort, where the ground may have settled or collapsed slightly over the roof of the buried structure.