That is not a metaphor or a quirk of modern land use; the two features are genuinely linked in the landscape, one folded behind the other, so that the sacred water and the subterranean darkness share the same small patch of north Kerry ground. It is the kind of arrangement that stops you assuming these things were ever entirely separate concerns.

A souterrain is a man-made underground passage or chamber, typically dry-stone lined, associated with early medieval settlement in Ireland. They were used variously for storage, refuge, and ventilation of nearby structures. The system at Knockane was examined by the Kerry Field Club in 1939, and what they found was more complex than a simple tunnel. The main passage branches into two arms, widening at several points along the way, with blind tunnels and small nooks opening off the principal route. The central chamber is sub-circular in plan, roughly 1.82 metres high and 1.2 metres in diameter, which is just enough space to stand upright and take stock. Parts of the tunnel have since collapsed, which means the full extent of the system is difficult to trace and some of those branching passages now lead nowhere in any practical sense.

Access today follows the same route recorded after the 1939 visit: over the holy well, then into the tunnel beyond. The collapsed sections mean the experience is fragmentary rather than complete, and the blind passages add a mild disorientation. Visitors should expect confined spaces and uneven ground underfoot rather than a preserved or managed interior.