This one is remarkable for what cannot be found. In the marshy pastureland of Knockroe in County Clare, a possible crannog, an artificial or partially artificial island built in a lake or wetland, typically during the early medieval period as a defended dwelling, was recorded as a raised mound roughly 24.5 metres in diameter and about 2 metres in height. When inspectors returned to the site in May 1999, they could not locate it. No trace of it appears on aerial imagery either. A place that may once have been a small island of human habitation has quietly dissolved back into the bog.

The site was first documented by Ó Riordáin in 1966 to 1967, who noted its position approximately 70 metres to the east of a separate, confirmed crannog nearby. At the time of that earlier record, the mound was overgrown with briars and other vegetation, suggesting it had already been long abandoned and left to its own devices. Whether it was ever definitively a crannog, rather than a natural or agricultural mound of some kind, was never fully established. That uncertainty, combined with its subsequent disappearance from the visible landscape, leaves it in an unusual category, a site that is officially recorded but practically gone, neither confirmed nor dismissed.