Which formation of basalt columns in Northern Ireland is a UNESCO World Heritage Site?

The Giant's Causeway is the UNESCO World Heritage Site formed by basalt columns on Northern Ireland's north coast.

Located in County Antrim near Bushmills, the site contains roughly 40,000 interlocking columns. They formed around 50 to 60 million years ago, when cooling lava contracted and fractured into the distinctive polygonal shapes. Most columns are hexagonal, though four-, five-, seven-, and eight-sided examples also occur.

UNESCO inscribed the Giant's Causeway and Causeway Coast in 1986, recognizing both its dramatic scenery and its geological importance. The site helped scientists understand columnar basalt and the processes that shape volcanic rock.

Irish legend gives the formation a more heroic origin: the giant Fionn mac Cumhaill supposedly built a causeway toward Scotland. Fingal's Cave on Scotland's Staffa island has similar basalt columns, but it is not the Northern Irish UNESCO site. Organ Pipes is another basalt formation, while Devil's Tower is made of phonolite porphyry.