At Ballyfinnane in County Kerry, within an earthwork known as a rath, a possible souterrain was noted and then, in practical terms, lost. A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement, used for storage, refuge, or both. At Ballyfinnane, no trace of one is visible above or below ground today.

The record of this site rests almost entirely on a single observation made in the 1930s by a Captain D. B. O'Connell, who noted a possible souterrain within the rath. A rath is a roughly circular earthen enclosure, common across Ireland from the early medieval period, which typically enclosed a farmstead or small settlement. Whether O'Connell saw an opening, a depression, or something more substantial is not recorded, and the cautious word "possible" has followed the site ever since. Nothing remains to verify or contradict what he saw.