First reported to the National Museum of Ireland in 1956, this underground stone passage stretches approximately 14 feet in length, descending 4 feet below ground level with walls about 3 feet wide. What makes this particular souterrain intriguing is its unusual architecture: halfway along the passage, it constricts dramatically to just 2 feet 2 inches before opening up again, creating a bottleneck effect that may have served defensive purposes or controlled access to stored goods.

The initial survey suggested this wasn’t an isolated structure but rather part of a larger underground complex. Evidence pointed to additional chambers branching off from the main passage, though these potential extensions remain unexplored. Such souterrains, found throughout Ireland, were typically used between the early medieval period and the 12th century as storage facilities, temporary refuges, or both. They represent remarkable feats of construction, built without mortar yet sturdy enough to survive over a millennium.

Perhaps the most tantalising discovery from the Clashygowan souterrain is an inscribed stone slab, reportedly found within the passage and now held in a private collection. The nature of these inscriptions remains a mystery, as the stone hasn’t been properly studied or documented since its removal. This artefact could potentially offer valuable insights into who built the souterrain, when it was constructed, or what purpose it served in the daily life of medieval Donegal.