Despite its appearance on both the first and second editions of the six-inch OS maps, modern archaeological surveys have found no physical evidence of this subterranean feature. The site sits where bedrock approaches the surface, positioned strategically on the edge of a plateau that commands sweeping views across the landscape to the south and west.

The disappearance of this cave remains something of a local puzzle. Whether it collapsed naturally over time, was deliberately filled in, or perhaps was misidentified by early surveyors, we may never know. The Archaeological Survey of County Donegal, compiled in 1983 by Brian Lacey and his team of researchers, documented this absence whilst cataloguing the county’s archaeological heritage from the Mesolithic period through to the 17th century. Their comprehensive work noted many such discrepancies between historical records and present-day remains, highlighting how Ireland’s archaeological landscape has changed over the centuries.

The location’s elevated position would have made it an ideal spot for a souterrain, those distinctive underground passages that dot the Irish landscape and typically date from the early medieval period. These structures served various purposes; storage chambers for food, hiding places during raids, or ritual spaces connected to ringforts and other settlements. While the Tullydonnell Upper cave may be lost to time, its documentation in early maps ensures its place in the historical record, a reminder that not all of Ireland’s archaeological treasures survive into the present day.