On the coast of Northern Ireland, in County Antrim, lies the Giant's Causeway.

An excerpt from the article 39 facts about Ireland

It is an original rock formation consisting of 37.000 tightly packed basalt columns that were formed during a volcanic eruption 50-60 million years ago. The tallest columns are about 12 meters high. The average width of the basalts is about 46 cm, the height is from 1 to 2 meters. At its widest point, the causeway is 180 meters wide and extends into the sea to a distance of 150 meters.