The hollow is the collapsed remains of a souterrain, an underground stone-built passage, typically associated with early medieval ringforts and thought to have served as a place of refuge, storage, or both. Moss-covered stones push out from its sides, and loose rubble lines the base, the remnants of chambers that have long since lost their roofs to gravity and time.

The depression extends some 21.5 metres in total, bending at a sharp angle to form its characteristic L-shape. The longer arm runs east to west, roughly 13 metres in length and up to a metre deep, narrowing noticeably at its eastern end to around 1.8 metres. At that narrowing, faint traces suggest a creep, the deliberately tight constriction built into souterrains to slow down anyone attempting to force entry, a small but telling detail about the anxieties of whoever constructed it. Beyond that point, the passage turns sharply southward and continues for a further 8.5 metres before merging into the slope of the ringfort's enclosing bank. Two large whitethorn bushes, one at the northwest limit and one at the southeast, have rooted themselves into the sides of the depression, framing the outline and, in the way of whitethorn on old earthworks, quietly insisting that something significant lies beneath.