A souterrain is a man-made underground structure, typically stone-lined, built during the early medieval period and associated with nearby settlement enclosures such as ringforts; they are thought to have served as refuges, cool-storage spaces, or both. What remains accessible here is only a portion of what once existed, which gives the site a curiously unresolved quality, as if the ground itself is withholding something.

A plan drawn up by Costello in 1902 recorded the souterrain as roughly L-shaped and comprising at least two chambers. Today, a stone-lined hollow roughly two metres long leads into a single accessible chamber running south-east to north-west, measuring around 3.9 metres in length and 1.2 metres wide. At its north-west end, a feature known as a creep is visible; a creep is a deliberately low, narrow connecting passage between chambers, presumably designed to slow or hinder unwanted entry. Beyond this, a second probable chamber can be glimpsed through a gap in the roof lintels, apparently turning south-west, though it cannot be entered. A second souterrain lies approximately 24 metres to the north-west within the same ringfort complex, suggesting the enclosure was once considerably more elaborate underground than it appears above ground today.