The Giant's Causeway is an area of approximately 40,000 interlocking basalt columns, formed as a result of an ancient volcanic fissure eruption. The tops of the columns form stepping stones that lead from the cliff foot and disappear under the sea. The majority of the columns are hexagonal in shape, though there are also some with four, five, seven or eight sides. The tallest of these formations stand at approximately 12 meters in height, with the solidified lava in the cliffs reaching a thickness of 28 meters in certain areas.