This one in Mulroog, County Galway, offers nothing of the sort. What is recorded here is an absence, a place where a souterrain may once have existed and has since left no mark on the ground whatsoever.

A souterrain is an underground passage or chamber, typically built during the early medieval period in Ireland, usually associated with a nearby ringfort or cashel and used for storage, refuge, or both. In this case, local knowledge points to the interior of an adjacent cashel, a type of stone-walled enclosure common across the west of Ireland, as the probable location. Whether the souterrain was ever fully constructed, subsequently collapsed, or was simply dismantled over the centuries is not known. No visible surface trace survives, which places this site in an odd category: a feature recorded not because anything can be seen, but because the memory of it persisted long enough to be noted.