Hi, young Albert!
I visited the Giant's causeway last October with my sister who was visiting from England.
According to Irish Mythology, the columns are the remains of a causeway built by the Irish giant, Fionn mac Cumhaill (Finn MacCool) who had been 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 giants could meet. Different versions of the myth differ as to who was the eventual victor. In one story, Fionn hid from Benandonner when he realised that his foe was much bigger than him. Fionn's wife, Oonagh, disguised Fionn as a baby and tucked him in a cradle. When Benandonner saw the size of the 'baby', he reckoned that its father, Fionn, must have been a giant among giants, and fled back to Scotland in fright, destroying the causeway behind him so that Fionn would be unable to chase him down.
The Giant's Causeway is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic fissure eruption around 50 to 60 million years ago. Most of the columns are hexagonal, although there are also some with four, five, seven or eight sides. The tallest are about 12 metres (39 ft) high, and the solidified lava in the cliffs is 28 metres (92 ft) thick in places.
It was declared a World Heritage Site by UNESCO in 1986, and a national nature reserve in 1987 by the Department of the Environment for Northern Ireland. In a 2005 poll of Radio Times readers, the Giant's Causeway was named as 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.