Local tradition holds that a souterrain, an underground stone-lined passage typically built during the early medieval period for storage or refuge, lies buried in the north-east corner of the field. No visible trace of it survives at the surface. The ground gives nothing away.

The site was recorded in C. Toal's North Kerry Archaeological Survey, published in 1995, where it appears as an isolated example known only through oral tradition rather than physical evidence. That distinction matters. Many souterrains across Ireland have been identified through collapse features, protruding lintels, or the slight depressions that betray a subterranean void. Here, there are none of these. What remains is essentially a place-memory, the local knowledge that something once lay underground, passed along without the confirmation of stone or soil.

That a site can be recorded, catalogued, and discussed while simultaneously being invisible is one of the quieter puzzles of Irish field archaeology. Knoppoge's souterrain, if it exists, belongs to a category of places that are more rumour than ruin, present in the archive but absent from the landscape.