Built by Sir Thomas Ruadh Fitzgerald, eldest son of the 14th Earl of Desmond, the castle saw considerable action during Ireland’s turbulent 17th century. It withstood an unsuccessful assault by James Fitz Morris in 1642 before falling to Lord Castlehaven three years later. A tragic accident in 1653 saw the castle burn, killing three daughters of its steward, Edward Germaine. The structure underwent repairs by Richard Boyle around 1620 and later restoration work by A.G.L. L’Estrange in the late 19th century before eventually passing into state ownership.

The tower house measures 13.6 metres east to west and 9.6 metres north to south, surviving to its full original height. Visitors entering through the eastern ground floor door would have once encountered a yett; an iron grille that protected the timber door, with the yett-hole still visible on the southern side. A spiral stone staircase in the southeast corner connects all five levels, each containing a main chamber alongside smaller mural chambers built into the thick walls. The architectural details reveal sophisticated medieval craftsmanship: windows feature two-part embrasures with wicker-centred vaults, whilst upper floors display elegant ogee-headed lights. The fourth floor is particularly impressive, featuring a wide rounded arch at its eastern end and a machicolation that provided defensive coverage over the main entrance below.

Each floor served different purposes, evident from their varied features. The ground floor chamber, lit by multiple windows, likely served as storage, whilst upper floors contained fireplaces, garderobes, and increasingly elaborate window designs; including double lights on the upper levels. The castle’s defensive elements remain visible throughout: narrow slit windows for archers, thick walls housing hidden chambers, and a wall walk along the top that once featured merlons, though these are modern reconstructions. Near the northwest corner, remnants of an ancillary structure survive, probably part of the original bawn enclosure that would have protected the castle’s courtyard. Now designated as National Monument number 240, Conna Castle stands as one of Cork’s most complete examples of a late medieval tower house, its stone walls still commanding views across the valley after more than 450 years.