A souterrain, one of those underground passages that pepper the Irish landscape, was discovered here some time ago, though today no visible trace remains. These subterranean structures, built between the early medieval period and the 12th century, were typically used for storage, refuge, or ritual purposes; their exact function often varying from site to site.

The discovery of this particular souterrain adds to Donegal's rich tapestry of archaeological features, documented comprehensively in the Archaeological Survey of County Donegal. This survey, compiled by Brian Lacey and his team in 1983, catalogues the county's field antiquities from the Mesolithic period through to the 17th century, providing invaluable insights into thousands of years of human activity in the region. The Tully More souterrain represents just one of many such hidden structures that once formed part of early medieval settlement patterns across the county.

While the souterrain itself has vanished from view, possibly filled in or collapsed over time, its documented existence serves as a reminder of the hidden history beneath Ireland's pastoral landscapes. The rolling grazing land that now characterises the site gives little indication of the underground chamber that once existed here, yet such invisible monuments are remarkably common throughout rural Ireland, waiting to be rediscovered or remembered only through archaeological records.