This is a souterrain, an underground chamber or tunnel built during the early medieval period, typically beneath or beside a defended enclosure. They were used variously for storage, refuge, or ventilation of a dwelling above, and dozens survive across Munster, though most remain poorly understood. What makes this one quietly arresting is precisely what limits our knowledge of it: it is inaccessible, sealed beneath the landscape, its full extent unknown.

The souterrain sits within the cashel at Ráth Ghaiscígh, a ringfort-type enclosure built of stone rather than earthen banks. Cashels of this kind were the farmsteads and defended homesteads of early medieval Ireland, their occupants typically farmers or minor lords. The lintelled entrance here, where large flat stones were laid across the top of a passage to form a roof, is characteristic of souterrain construction across the island. A second depression lies a short distance to the southeast of the first, suggesting either a further chamber or a separate section of the same underground system. Whether the two features are connected has not been established, and the site has not been excavated in any recorded modern investigation.