The Giant's Causeway is an area of about 40,000 interlocking basalt columns. The formation is a result of an ancient volcanic eruption. It is in County Antrim on the northeast coast of Northern Ireland. It is a World Heritage Site by UNESCO. It was named 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.