The structure linking Feenish Island with the neighbouring island of Inishmacnaghtan is roughly 150 metres long and about two metres wide, built from a double row of boulders packed with infill material. For most of the tidal cycle it lies submerged, and for a brief window it becomes a walkable, if wet, crossing.

What makes the structure quietly interesting is that its origins and precise age remain unrecorded. It appears on the second edition Ordnance Survey map, which places it firmly in the nineteenth century at the latest, and the earlier six-inch OS map names it simply as a ford, suggesting that surveyors were uncertain whether to classify it as a built feature or a natural crossing improved by human hands. That ambiguity is not unusual for these low-lying coastal zones along the west of Ireland, where generations of island communities engineered practical connections between landmasses using whatever stone lay to hand, and where the resulting structures can be difficult to date or attribute with confidence. The double-boulder-and-infill technique described by O'Sullivan and colleagues in 2010 is a recognisable form of causeway construction, functional rather than monumental, designed to provide reliable footing across a tidal channel without requiring elaborate engineering.