Giant’s Causeway

About 40,000 interlocking basalt columns left by a fissure eruption in the Paleogene, part of the North Atlantic Igneous Province. Most are hexagonal, though some have between four and eight sides; the tallest stand around twelve metres, and the solidified lava in the cliffs behind runs twenty-eight metres thick in places. Their tops make stepping stones running down from the foot of the cliff and out under the sea. UNESCO listed the site in 1986 and it became a national nature reserve the year after. Access is free, the visitor centre that charges a fee can be walked past.