This underground structure, which appeared on the 2nd edition of the Ordnance Survey 6-inch map, was situated on good grazing land that sloped gently towards the northwest. Though the cave has long been filled in, its former presence speaks to the rich archaeological heritage hidden beneath Donegal’s verdant fields.

Souterrains, or artificial underground passages, are found throughout Ireland and were typically constructed during the early medieval period, roughly between the 6th and 12th centuries. These subterranean structures served various purposes; some functioned as storage spaces for food and valuables, whilst others provided temporary refuge during raids. The Ballylosky example would have been carved into the earth or constructed with stone walls and lintels, creating a network of chambers and passages beneath the surface.

The documentation of this lost souterrain comes from the Archaeological Survey of County Donegal, a comprehensive catalogue compiled by Brian Lacey and his team of archaeologists in 1983. This survey represents one of the most thorough attempts to record Donegal’s field antiquities, spanning from the Mesolithic period through to the 17th century. Though the Ballylosky souterrain can no longer be explored or studied directly, its inclusion in historical maps and archaeological records ensures that this piece of Ireland’s underground heritage isn’t entirely forgotten.