The depression sits close to the inner face of the bank of Lisnaclea rath, a rath being a roughly circular earthwork enclosure used as a farmstead during the early medieval period in Ireland, typically dating from around the fifth to the twelfth centuries. What makes this particular feature of interest is its form: three branches meeting at a point, the longest running northeast to southwest at about five metres, the second aligned northwest to southeast at just over three metres, and a short vertical leg of two metres completing the shape. Together, these suggest the collapsed or infilled remains of a souterrain.

A souterrain is an underground stone-lined passage or chamber, built by hand and typically associated with raths and ringforts across Ireland. Their exact purposes are still debated, but they are generally understood to have served as places of refuge, cool storage for dairy produce, or both. The Y-shaped plan at Lisnaclea is somewhat unusual; most souterrains follow a simpler linear or slightly curving route, occasionally with a single side chamber. A branching, forked arrangement is less common and adds a degree of curiosity to what is otherwise an unassuming hollow in the earth. The dimensions recorded are modest throughout, with the depression reaching no more than about a metre in depth along its deepest branch, which points to either significant collapse or considerable silting over time. The phrasing used by those who recorded it is careful: the depression "may represent" a souterrain site, meaning the underground structure itself, if it ever existed in the form suggested, has not been excavated or confirmed through investigation.