Known as Bully's Acre, it contains the shaft of a high cross dated to somewhere between the 9th and 11th centuries, a carved stone fragment that hints at a monastic community long since vanished. High crosses were among the most significant monuments of early medieval Irish Christianity, typically erected at important ecclesiastical sites as focal points for prayer and assembly. That this shaft survives here at all is remarkable, given what the ground around it has absorbed over the centuries.

The monastery in question is almost certainly 'Cill Maignenn', the early Christian foundation that gives Kilmainham its name. Scholarly consensus places it as a 7th-century establishment associated with St. Maignenn, and this western edge of the Royal Hospital grounds is considered its most likely location. For much of its later life, the site served as a paupers' graveyard. In 1760, General Dikes, then Commander of the Forces in Ireland, had the ground levelled and enclosed within a stone wall, imposing a degree of order on a place that had long been a burial ground for the poor and the anonymous. The graveyard was closed for new interments following the cholera epidemic of 1832, a crisis that overwhelmed burial sites across Dublin and prompted authorities to restrict where the dead could be laid. The ground continued to give up its occupants even after closure; during the construction of a water main into the Royal Hospital via the western avenue, human burials were uncovered, confirming just how densely the site had been used.

Bully's Acre sits within the grounds of the Royal Hospital Kilmainham, now home to IMMA, the Irish Museum of Modern Art. The graveyard is accessible to visitors exploring the wider grounds, which are open to the public. The high cross shaft is the principal feature to look for, a worn but legible reminder of what preceded the 17th-century hospital building and every subsequent use of this land. The stone wall enclosure put up by General Dikes still defines the space. It is a quiet corner, easy to pass without a second glance, but worth pausing at if you know what lies beneath.