This underground chamber, measuring 1.7 metres in length and oriented northwest to southeast, was carefully constructed using drystone walling techniques that have endured for centuries. The builders created a space tall enough for a person to stand upright, roofing it with flagstones in a method typical of Irish souterrains from this period.

These subterranean structures, found throughout Ireland but particularly common in Ulster, were likely built between the 6th and 12th centuries AD. Souterrains served multiple purposes for early Irish communities; they functioned as storage spaces for food and valuables, provided refuge during raids, and maintained consistent cool temperatures ideal for preserving dairy products and grain. The Ardagh souterrain's modest size suggests it may have belonged to a single farming family rather than a larger settlement.

Unfortunately, this intriguing glimpse into Donegal's past is no longer accessible to visitors, though its existence was documented during the comprehensive Archaeological Survey of County Donegal conducted by Brian Lacey and his team in 1983. The survey, which catalogued field antiquities from the Mesolithic period through to the 17th century, ensures that even inaccessible sites like this souterrain remain part of the historical record, preserving knowledge of how our ancestors adapted to and shaped the Irish landscape.