Located just west of Dundalk, Castletown Mount — often known locally as Cú Chulainn’s Castle – is a hill long associated with myth and legend. In Irish tradition, the site is linked to Cú Chulainn, who is said to have been born here and raised in a fortress that once stood on the summit, overlooking what is now the modern town. While these associations belong firmly to heroic mythology rather than archaeology, they reflect the deep cultural importance of the hill in local tradition.

In 1790, a wealthy merchant named Patrick Byrne built a mansion on the mount, reputedly on or near the remains of an earlier Norman motte-and-bailey structure. Today, only part of Byrne’s house survives – a ruined tower known locally as “Byrne’s Folly.”

Byrne developed a fearsome reputation in the area. He was widely believed to be involved in smuggling, and may also have engaged in privateering – a semi-legal form of piracy tolerated by the Crown so long as British ships were not attacked and a share of the profits was handed over to the authorities. His wealth and isolation made him a frequent target for robbery.

One story claims that three men once crept into his bedroom intending to rob him, but that Byrne persuaded them to leave with promises of reward. When they departed, he allegedly alerted the authorities, and the men were later arrested and executed – a tale often cited as evidence of his cunning and ruthlessness, though it survives only in local tradition rather than official record.

According to folklore, Byrne eventually hid his fortune in a cave beneath the mount. To protect it, he was said to have made a pact with dark forces, who provided a phantom black cat as a guardian. This creature was described as having glowing eyes and the ability to grow to enormous size when threatened. The cat is still said to prowl the hill at night, guarding Byrne’s buried treasure, which – if legend is to be believed – has never been recovered.

Today, Castletown Mount stands as a rare blending of heroic mythology, 18th-century history, and supernatural folklore, with the ruined tower of Byrne’s Folly serving as a visible reminder of both its turbulent past and its enduring legends.