It cannot be seen. There is no depression in the grass, no obvious entrance, no stone-lined mouth. The only reason anyone knows it is there at all is that, in 1924, someone pushed a crowbar into the ground and found nothing solid beneath.

A souterrain is an underground passage, typically stone-lined and roofed with large flat slabs, built during the early medieval period as a place of refuge, storage, or concealment, often beneath or beside a ringfort, the circular earthen or stone enclosures that once served as farmsteads across Ireland. The Clonleigh example was investigated by a researcher named Cremen, who noted what looked like a slightly raised pathway extending from the ringfort across the field. Following it with a crowbar confirmed that the ground was hollow underneath, consistent with a covered underground passage. The far end of this apparent route terminated near a group of pillar stones, a separate monument in its own right. Cremen was confident enough to declare it a souterrain, though later assessment has left open the possibility that what he probed was actually a flagged field drain, the kind of covered stone channel used to manage waterlogged agricultural ground. The two structures are not always easy to distinguish from the surface, or from the end of a crowbar.

Today there is no visible surface trace of the feature. The ringfort it belongs to still exists, but the souterrain, if that is what it is, lies quietly underneath pasture, its hollow interior intact or collapsed, unexcavated and unconfirmed.