A souterrain, one of Ireland's enigmatic underground passages, was documented here in 1967 by the National Museum of Ireland. These subterranean structures, found throughout Ireland and Scotland, were typically built between the early medieval period and the 12th century, serving as storage spaces, refuges, or perhaps holding ritual significance for the communities that constructed them.

When surveyors returned to catalogue Donegal's archaeological heritage for the comprehensive 1983 survey, they found no trace of the Lackagh souterrain. Whether it had collapsed, been filled in, or perhaps was misidentified in the original report remains unknown. The surrounding landscape, characterised by rough, uncultivated terrain, offers no visible clues to its whereabouts; the earth has seemingly reclaimed whatever secrets lay beneath.

This vanishing act isn't unique in Irish archaeology, where many sites recorded in earlier surveys have since disappeared through natural deterioration, agricultural activity, or development. The Lackagh souterrain joins a growing list of 'lost' monuments across Donegal, each one a reminder of how fragile our archaeological heritage can be. Its story, preserved only in survey notes and museum records, speaks to the importance of documentation in archaeology; sometimes, the written word becomes the only evidence that these ancient structures ever existed at all.