The Hexagons - Giant's Causeway is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic eruption. Located in Northern Ireland, it was declared a World Heritage Site by UNESCO in 1986. 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 there are also some with four, five, seven or eight sides. Image by Thomas Mader.