Montpelier Hill in the Dublin Mountains is the site of the Killakee House (also known as the Stewards House) and the ruins of the notorious Hellfire Club, a hunting lodge built around 1725 by Speaker of the Irish House of Commons William Conolly. The lodge was later used by the Irish Hellfire Club, an 18th-century society of debauched aristocrats who engaged in drinking, gambling, and allegedly Satanic rituals. The ruins sit on a cairn that may have been a prehistoric passage tomb, and locals have long believed that the destruction of the cairn during the lodge's construction unleashed supernatural forces.
The site has been one of Ireland's most intensely haunted locations for centuries. Visitors report seeing a massive black cat with glowing eyes prowling the ruins — according to legend, a cat was set ablaze during a Hellfire Club ceremony and has returned as a spectral beast. Full apparitions of men in 18th-century finery have been reported, as have disembodied screaming, the smell of sulphur, and the sensation of extreme dread.
In the 1970s, the artist Margaret O'Brien, who lived in Killakee House, reported extensive poltergeist activity and encounters with a spectral dwarf figure that terrorized her household. The site's elevation above Dublin, with panoramic views of the city and Dublin Bay, creates a commanding but deeply unsettling atmosphere.