A souterrain is an underground passage or chamber, typically cut into the earth or lined with stone, associated with early medieval ringforts and thought to have served for storage, refuge, or both. The one at Mylane is notable precisely for its absence from view: there is no visible surface trace, only a tradition of local knowledge and a handful of partly filled holes that once hinted at something underneath.

The record of this site is a layered thing, assembled from two quite separate moments of inquiry. Around 1865, the Anglo-Irish general and ethnologist Augustus Henry Lane Fox, later known as Pitt-Rivers, investigated earth-cut chambers he described as unrevetted, meaning they lacked any stone lining and were simply hollowed from the ground, in two ringforts in the Mylane area. Which ringforts he examined has never been firmly established. Then in 1939, a researcher named Hartnett noted a local account of a cave in the southern half of one particular ringfort, and observed several partly filled depressions in the ground as circumstantial evidence. Whether Pitt-Rivers and Hartnett were looking at the same place, or at different ones entirely, remains unresolved.

That uncertainty is part of what makes the site quietly interesting. The archaeology here is not a matter of a monument you can walk around and photograph but of inference, of an underground space known mainly through hearsay and subsidence. The ringfort itself survives at Mylane, but the souterrain beneath it, if it is still intact at all, keeps its own counsel.