The first rediscovery happened around the 1940s or 1950s, when a gravel pit was being dug in the area and workers broke into something stone-built and deliberate underground. The pit was filled in, the chamber resealed, and the matter appears to have been set aside. It was not until the mid-1970s that the structure was found again, and even then it had left no trace on any Ordnance Survey historic mapping and could not be spotted from the air.

A souterrain is an underground stone-built passage or chamber, typically associated with early medieval settlement in Ireland, and thought to have served for storage, refuge, or both. The Corkan example, as it was recorded in 1977, is a rectangular chamber running east to west, roughly 6.6 metres long, between 1.87 and 3 metres wide, and 1.75 metres high. The drystone walls are laid in regular courses of rubble limestone, rising almost vertically before giving way to two or three courses of slight corbelling near the roof, where seven large lintels complete the cover. A secondary blocking wall of rougher, unbonded stonework fills off the eastern end, probably added at some point to shore up a weakness in the roof. The original entrance, a narrow lintelled opening at the north-east corner, has been closed by collapse and may have been deliberately shut when the blocking wall went up; the way in now is through a hole in the roof. Two small rectangular recesses are cut into the western wall, one of which the later blocking wall had sealed off until a hole was made through it. The floor has been disturbed by digging at various points. Among the loose material inside, the most arresting object is a large inscribed stone lying in the centre of the floor, marked with what appears to be the letter U and a possible I. Scattered animal bones, teeth, flecks of charcoal, and a small button found just outside one of the wall recesses suggest that the chamber's long, interrupted history of use does not end with whoever first cut it into the hillside. The site sits within 700 metres of a cluster of related early monuments, including the remains of a church, an abbey, and an ogham stone to the west, suggesting this corner of Westmeath was once considerably busier than it looks today.