The structure has never been excavated and exists now only as a faint signature beneath the grass, detectable by instruments rather than the eye.

The Civil Survey of 1654 to 1656, a detailed land assessment carried out in the aftermath of the Cromwellian conquest, recorded a masonry-built feature described simply as a 'Mount' positioned outside the main gatehouse of the castle. The entry is precise enough to carry weight: roughly 32 feet by 30 feet, built entirely of stone, sitting just beyond the gate. A Confederate-era bastion is the most plausible interpretation. The Confederation of Kilkenny, the Catholic assembly that governed much of Ireland between 1642 and 1649, used the town as its political capital, and the castle itself was a key stronghold. A projecting stone bastion at the gatehouse would have been a logical addition during that period, providing flanking defence against artillery or assault from the east. A geophysical survey carried out in 2010, covering the parkland to the east of the castle, identified a rubble spread and possible structural remains approximately 45 metres outside the gatehouse, which may correspond to what the Civil Survey was describing. Geophysical survey works by detecting variations in the ground's electrical resistance or magnetic properties, allowing buried walls and disturbed soil to show up without any digging.