This underground passage, marked on 19th-century Ordnance Survey maps as ‘Cashel’, has suffered considerable damage over the years, though remnants of its original T-shaped structure remain accessible. What survives is a narrow tunnel measuring approximately 1.8 metres wide and just 0.6 metres high, with about 1.9 metres currently open for exploration. The construction technique, using large stone slabs for both walls and ceiling, exemplifies the dry-stone building methods employed across Ireland during the early Christian period.

The site occupies a partly artificial platform carved into the hillside, suggesting deliberate landscaping by its original builders. First documented by G.H. Kinahan in 1889, who noted its distinctive T-shaped layout, the souterrain would have served multiple purposes for the local community; these underground chambers typically functioned as storage facilities for valuable goods, refuges during raids, or possibly held ritual significance. The surrounding landscape of rich pasture indicates the area has been continuously farmed for centuries, with the souterrain bearing silent witness to generations of agricultural activity above.

Though much of the original structure has been lost to time and the elements, what remains provides valuable insights into the engineering skills and daily concerns of Ireland’s early medieval inhabitants. The Archaeological Survey of County Donegal, compiled in 1983, ensures that even fragmentary sites like this one are documented for future generations, preserving knowledge of these remarkable underground structures that dot the Irish countryside.