But when the ground gave way in a field at Miles in County Cork, it opened into something that had been sealed underground, undetected, for well over a thousand years. What emerged was a souterrain, an early medieval underground structure of the kind that appears across Ireland, typically associated with ringforts or enclosures and thought to have served as refuges, storage spaces, or both. The Miles example is particularly elaborate, consisting of three separate earth-cut chambers, each roughly beehive-shaped in cross-section, connected by low, narrow passageways known as creepways.

Documented by Kiely in 1995, the souterrain sits within the northern half of an enclosure and was entered, initially at least, through the collapsed roof of the first chamber, which lies about 1.3 metres below ground level. That first chamber measures roughly 3.2 metres in one direction and leads, via two separate creepways, into the other two chambers. The dimensions throughout are tight; the creepways range from about 0.5 to 0.75 metres wide, meaning that anyone moving between chambers would have done so on hands and knees. Chamber 3 is particularly interesting because bedrock breaks through the floor in two places, forcing one of the outgoing creepways to begin nearly 0.6 metres above floor level to clear it. Several creepways leading from this third chamber are now blocked, some with sandstone slabs and others obscured by fallen earth, and it is possible that the network was once more extensive than what survives. Construction shafts, the vertical tunnels dug to allow builders to excavate the chambers from above before being sealed over on completion, are visible in two places. Local tradition holds that a second souterrain lies about 175 metres to the south-east, which, if confirmed, would suggest this part of Miles was once a more substantial early medieval settlement than the surface currently implies.