Castleknock Castle, now a ruin overlooking the modern village of Castleknock, was originally built by the Normans toward the end of the 12th century. It stood on an earthen mound traditionally believed to have been the site of an earlier royal residence and possibly an ancient tumulus, suggesting the location held significance long before the Normans fortified it.

Over the centuries, the castle passed through several hands, including the powerful Tyrrell family, who were associated with Castleknock during the medieval period. It is from the 14th century that the site gains its most enduring and tragic legend – that of “The White Lady of Castleknock.”

According to local folklore, the White Lady is the restless spirit of Eibhleen O’Brinn (O’Byrne), daughter of a Wicklow chieftain. The story tells that during the 1300s Castleknock Castle was home to two brothers, John Tyrrell and Richard Tyrrell, the sixth Baron. Richard is portrayed in tradition as honourable, while John is remembered in darker terms – violent, cruel, and feared throughout the surrounding area.

When Richard was away from the estate, John is said to have terrorised neighbouring families. One of his most notorious alleged crimes was the abduction of the beautiful Eibhleen O’Brinn, whose father lived south of Chapelizod near Ballyfermot Hill. She was taken to Castleknock and imprisoned within its walls.

One night, hearing footsteps approaching her room and fearing the worst, Eibhleen chose to take her own life rather than suffer whatever fate awaited her. Using the pin of her gown, she opened a vein and bled to death in the darkness.

Meanwhile, her father had rallied his followers and mounted an attack on Castleknock in an attempt to rescue her. John Tyrrell was killed in the fighting, but their efforts came too late; Eibhleen was already dead.

For generations afterward, locals claimed that her spirit lingered at the ruined stronghold. The White Lady, dressed in a flowing robe, was said to appear at midnight, drifting slowly along the castle walls, her mournful wail echoing across the hill as she lamented her tragic end.

As with many medieval ghost stories, the tale blends fragments of historical figures with folklore, and no contemporary 14th-century record of the event survives. Nonetheless, the legend of the White Lady of Castleknock remains one of Dublin’s longest-told supernatural traditions, passed from one generation to the next.