Photograph of the Great Causeway in County Antrim. In the foreground are rocks standing in vertical formations.  

Popular folklore recounts how the Causeway was constructed by the Irish Giant Fionn mac Cumhaill in order to traverse the Irish Sea to meet his adversary, the Scottish Giant named Benandonner so that they could fight. 50 million years ago, intense volcanic eruptions produced molten basalt that cooled to produce pillar like formations that form the causeway that exists today.