It measures roughly 9.3 metres by 8.1 metres, oriented to the northwest, and its relationship to the structures around it raises a question that has not been cleanly resolved: was it built as an extension to the tower's outer wall, or as a later addition squeezed into the angle where the bawn met the castle? The uncertainty is part of what makes it interesting.

The building sits within a wider complex two fields to the north of Graystown Castle, on a low rise of rock outcrop with open views in every direction. Scattered across the same grassland are the footings of a rectangular tower, two separate bawns, a house, and two further outbuildings, all reduced now to low grassy mounds. A bawn, in Irish castle-building tradition, was a walled enclosure adjoining a tower house, used to protect livestock and provide a defensible yard. To the south lies a deserted medieval settlement, making the whole area something of a palimpsest of occupation, each phase leaving only its lowest course behind. The building in question sits immediately to the northwest of the western angle of one of those bawns, appearing to have been constructed up against both the bawn wall and the outer face of the tower's northwest wall. Whether it preceded the enclosure or followed it remains unclear.