The Giant's Causeway () is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic fissure eruption. It is located in County Antrim on the north coast of Northern Ireland, about northeast of the town of Bushmills.
It was declared a World Heritage Site by UNESCO in 1986 and a national nature reserve by the Department of the Environment for Northern Ireland in 1987. In a 2005 poll of Radio Times readers, the Giant's Causeway was named the fourth-greatest natural wonder in the United Kingdom.
The tops of the columns form stepping stones that lead from the cliff foot and disappear under the sea. Most of the columns are hexagonal, although some have four, five, seven, or eight sides. The tallest are about high, and the solidified lava in the cliffs is thick in places.
Much of the Giant's Causeway and Causeway Coast World Heritage Site is owned and managed by the National Trust. It is one of the most popular tourist attractions in Northern Ireland, receiving over 998,000 visitors in 2019. Access to the Giant's Causeway is free of charge: it is not necessary to go via the visitor centre, which charges a fee. The remainder of the site is owned by the Crown Estate and several private landowners.
Geology
Around 50 to 60 million years ago, during the Paleocene Epoch, Antrim was subject to intense volcanic activity, when highly fluid molten basalt intruded through chalk beds to form an extensive volcanic plateau. As the lava cooled, contraction occurred. Horizontal contraction fractured in a similar way to drying mud, with the cracks propagating down as the mass cooled, leaving pillarlike structures, which also fractured horizontally into "biscuits". In many cases, the horizontal fracture resulted in a bottom face that is convex, while the upper face of the lower segment is concave, producing what are called "ball and socket" joints. The size of the columns was primarily determined by the speed at which lava cooled. The extensive fracture network produced the distinctive columns seen today. The basalts were originally part of a great volcanic plateau called the Thulean Plateau, which formed during the Paleocene.
Geological heritage site
In respect of its key role in the development of volcanology as a geoscience discipline, and notably the origin of basalt, the Palaeocene rocks of the Giant's Causeway and Causeway Coast were included by the International Union of Geological Sciences (IUGS) in its assemblage of 100 "geological heritage sites" around the world in a listing published in October 2022.
Legend
According to legend, the columns are the remains of a causeway built by a giant. The story goes that the Irish giant Fionn mac Cumhaill (Finn MacCool), from the Fenian Cycle of Gaelic mythology, was challenged to a fight by the Scottish giant Benandonner. Fionn accepted the challenge and built the causeway across the North Channel so that the two could meet. In one version of the story, Fionn defeats Benandonner. In another, Fionn hides from Benandonner when he realises that his foe is much bigger than he is. Fionn's wife, Sadhbh, disguises Fionn as a baby and tucks him in a cradle. When Benandonner sees the size of the "baby", he reckons that its father, Fionn, must be a giant among giants. He flees back to Scotland in fright, destroying the causeway behind him so that Fionn would be unable to chase him down. Across the sea, there are identical basalt columns (a part of the same ancient lava flow) at Fingal's Cave on the Scottish isle of Staffa, and it is possible that the story was influenced by this.
Overall, in Irish mythology, Fionn mac Cumhaill is not a giant but a hero with supernatural abilities, contrary to what this particular legend may suggest. In Fairy and Folk Tales of the Irish Peasantry (1888), it is noted that, over time, "the pagan gods of Ireland [...] grew smaller and smaller in the popular imagination until they turned into the fairies; the pagan heroes grew bigger and bigger until they turned into the giants". There are no surviving pre-Christian stories about the Giant's Causeway, but it may have originally been associated with the Fomorians (Fomhóraigh); the Irish name Clochán na bhFomhóraigh or Clochán na bhFomhórach means "stepping stones of the Fomhóraigh". The Fomhóraigh are a race of mythological beings in Irish mythology who were sometimes described as giants and who may have originally been part of a pre-Christian pantheon.
Letitia Elizabeth Landon comments on these mythological associations in her notes to , a poetical illustration to a painting by Thomas Mann Baynes.