Built directly onto exposed bedrock, this limestone rubble fortress measures an unusual 16.2 metres from north to south and 11.35 metres from east to west, making it considerably longer than most Irish tower houses of its type. The castle’s substantial walls, ranging from 2.62 to 2.95 metres thick at the base, feature a pronounced batter that rises three metres high, though portions have been robbed away over the centuries.

The tower house, now heavily cloaked in ivy, survives only to the base of its first floor, with much of the internal wall facing stripped away by stone robbers. The original entrance was positioned towards the western end of the northwest wall, where remnants of a 1.3 metre wide lobby area can still be traced within the wall’s thickness. The ground floor was illuminated by three flat-headed windows with straight-sided embrasures; the best preserved examples in the northeast and southwest walls still retain their external flat lintels, whilst only the southeast window preserves its internal voussoirs. Multiple wall cupboards, each roughly 0.75 metres in width, height and depth, are built into all four walls, with an L-shaped example at the southern end of the southeast wall measuring 1.37 metres wide.

Historical records provide frustratingly little detail about Modesill Castle’s past. The Civil Survey of 1654-56 makes no mention of the castle itself, though it does record that James Tobyn of Killaghy Esq. and Pierce Butler of Callin Esq. were listed as proprietors of ‘Moddesshell & Graig’ in 1640. At the eastern end of the southeast wall, a garderobe chute measuring 0.9 by 0.98 metres provided medieval sanitation, exiting at ground level through an opening 0.75 metres wide and 0.89 metres high. Though time and neglect have taken their toll, the castle’s ruins still offer a fascinating glimpse into the defensive architecture of medieval Ireland, particularly in its unusual proportions and careful positioning just below the hilltop summit.