A cashel is a roughly circular or rectilinear stone enclosure, a form of defended settlement common across early medieval Ireland, and the one here survives in moderately good condition. What makes the arrangement at Lisheeneagh quietly interesting is this business of fitting a rectangular house inside an older structure, borrowing its corners and walls, making use of what was already standing.

The building measures eight metres east to west and 5.2 metres north to south. Where it survives well, along the east and south sides, it has a double-faced wall roughly 0.9 metres wide and 1.2 metres high, meaning a wall built with two distinct outer faces and rubble or fill between them, a standard construction technique. Elsewhere the wall has collapsed into spread stone. The building also projects slightly northward, about 1.8 metres beyond the line of the cashel's north wall, which suggests it was not simply inserted wholesale into a pre-existing space but adapted to particular needs or constraints. About seven metres to the north sit another rectangular building and a separate medieval architectural fragment, hinting that this was once a more substantial cluster of structures. Thomas Johnson Westropp, writing in 1915, considered the building relatively modern, but the current assessment is that it may date to the late medieval period, a reminder that a nineteenth-century scholar working without modern survey tools could reasonably mistake one era's stonework for another's.