The structure is defined by a bank of stone and earth, faced with stones set on edge, and measures roughly thirteen and a half metres long by nearly seven metres wide. What makes it quietly arresting is not its size but what lies beneath and around it: hollows in the interior floor are thought to indicate an extension to a souterrain, an underground stone-lined passage typically used in early medieval Ireland for storage or concealment, whose main entrance lies just to the north of the house. A later field wall, running east to west, cuts straight across the middle of the structure, one era of land use slicing through another without ceremony.

A cashel is a stone-walled ringfort, and Cahernahooan is one of many scattered across the limestone landscape of Clare. The house inside it has not been precisely dated, but its form offers a reasonable pointer. Researchers have noted its resemblance to a house excavated at Caherconnell cashel, a comparable site also in Clare, which was dated to somewhere between the fifteenth and seventeenth centuries. That comparison, drawn by Comber and Hull in 2010, suggests this was not an early medieval dwelling tucked inside an ancient enclosure, but something built or occupied considerably later, long after the cashel itself was first constructed. The reuse of old enclosures for later settlement was not unusual in this part of Ireland, where solid stone walls offered ready-made shelter and boundary even centuries after their original purpose had shifted.