This unassuming hollow, measuring roughly 1.5 metres across, is all that remains visible of a souterrain discovered at the start of the 20th century. The site sits near a cliff edge, surrounded by lush pasture lands that offer sweeping views across the Finn Valley.

Souterrains, meaning 'underground' in French, are mysterious subterranean structures found throughout Ireland, with particularly high concentrations in counties like Donegal. These man-made underground passages and chambers were typically built during the early medieval period, roughly between the 6th and 12th centuries. While their exact purpose remains debated amongst archaeologists, they likely served multiple functions; as storage spaces for food and valuables, temporary refuges during raids, or perhaps holding ritual significance for the communities that built them.

The Killygordon souterrain's location is particularly intriguing, positioned as it is with commanding views of the valley below. This strategic placement was common for such structures, often associated with ringforts or other early medieval settlements. Though the full extent of the underground chambers remains hidden beneath the manicured lawn of the house, the depression serves as a subtle reminder of the complex lives and ingenious engineering of Ireland's early medieval inhabitants who once called this landscape home.