Geology made this place defensible long before anyone needed it. The promontory drops away on its sides to the River Awbeg, the river that Edmund Spenser called Mulla in The Faerie Queene when he lived nearby at Kilcolman. The caves on the south bank of the Awbeg, like the flint scatter at Kilcummer, place humans here in the Mesolithic, about nine thousand years ago. Ring barrows and ring forts in the immediate fields trace the late Bronze and early Iron Ages, when Dun Cruadha rose as an inland promontory fort guarding the valley. A St Patrick's holy well still bubbles on the grounds. A Sheela na Gig, one of those weathered medieval carvings whose meaning still divides scholars, watches from the stonework. The site never quite stopped being a site.

The castle as it stands began in the late 12th century, when two Cambro-Norman brothers - Alexander and Raymond FitzHugh, grandsons of Maurice FitzGerald - built their fortress on the old Dun Cruadha foundations during the Norman Invasion of Ireland. The round tower at the eastern end dates from that period and still stands, though no longer accessible. When Alexander's daughter Synolda married David de la Roche, the surrounding territory became Roche Country, and the place was called Roche Castle. Over the next four hundred years the Roches added the 13th-century watch tower and sentry walk, the medieval defence walls, the 15th-century Norman keep. They commissioned the Book of Fermoy, a medieval manuscript still held by the Royal Irish Academy in Dublin. Through the Tudor reconquests, through the Desmond Rebellions and the destruction visited on so many Munster castles, the Roches held on.

It was Cromwell that ended the Roche tenure. In 1666, after the Cromwellian land settlements, the castle passed to Colonel John Widenham, and Roche Castle became Castle Widenham. The Widenhams were wealthy but politically quieter than the Roches had been, and that quiet probably saved the place. While other Munster castles fell to ruin through political collapse or military destruction, Castle Widenham was modified, extended, and lived in. The post-Cromwellian fortified house took shape in the 17th and 18th centuries, with a courtyard and outbuildings added, then modified again. The Widenhams kept the keys for almost three hundred years, into the 1960s, when Sir Delaval Cotter, 6th Baronet of Rockforest, and his wife bought the estate.

The Cotters held it for about a decade. Then came a string of owners and a rebranding as Blackwater Valley Castle, until in 1991 it passed to the Nordstrom Family Trust. The Trust took a particular view: the castle would have to pay for itself if its heritage was going to survive. So since 2005 it has been available for private hire, hosting castle weddings, private parties, and family gatherings. The courtyard houses an adventure centre called Blackwater Outdoor Activities. The 12th-century tower is still there. So is the medieval Sheela na Gig, the holy well, the keep, and the long sentry walk. The continuity is the point. Walk the grounds and you cross nine thousand years of human habitation in about ten minutes - a Mesolithic flint scatter under your feet, a Norman tower over your shoulder, and somebody's reception venue ahead through the gate.