A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts and thought to have served as a place of refuge, cool storage, or both. Here, the passage itself has long since collapsed, and what remains is essentially a depression in the ground, easy to miss and easier still to misread as nothing more than a dip in a field.

The ringfort into which this souterrain was built is recorded separately, and the two features were clearly conceived as a pair. A ringfort's fosse is the encircling ditch that runs outside the main rampart, and it was specifically on the inner side of this fosse that the souterrain was constructed, tucked against the base of the inner rampart wall. A researcher named Bowman, writing in 1934, recorded that fences already flanked the structure at that point and that it was then practically destroyed. The intervening decades have not been kind to what remained. His observation, though brief, is the only eyewitness account we have of the feature before the ground swallowed it almost entirely.