According to Wikipedia
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. 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 the fourth greatest natural wonder in the United Kingdom.
You can take a virtual tour of the Giant’s Causeway courtesy of the National Trust.