The Giant's Causeway is a floor: forty thousand columns of black basalt stepping down off a headland in Northern Ireland and disappearing under the Atlantic. The tops are worn flat and most of them are six-sided; up close you can trace the tight joints between them, and no two pillars are quite the same width. Nothing cut them. A thick sheet of lava cooled here and shrank as it hardened, cracking from the top down, and cracks that meet at about 120 degrees tile a surface into hexagons. Where it cooled unevenly the columns came out four-, five-, seven- or eight-sided. You cross the apron column to column, down to where it slopes into the sea. At the waterline on a rough day the swell bursts white over the outer stones, booms into the gaps and drains back through them with a hiss.
The cliff path above gives you what the shore withholds: from up there the whole formation reads as one honeycomb sheet, ringed by an amphitheatre of taller columns. From spring into summer the ledges are loud with nesting fulmars, kittiwakes and guillemots. Back on the stones, the last hour before dark is the one to stay for. The coaches have gone, and the low sun takes the basalt from grey to copper — the Giant's Organ, the tall bank of pillars behind the apron, first of all. The road has an older explanation than the lava. Finn McCool built it to reach Benandonner, a giant in Scotland, then got a proper look at his rival and ran home, tearing the road up behind him. The same columns do come back out of the sea at Fingal's Cave, on the Scottish island of Staffa. Generations of visitors have picked shapes out of the forty thousand and given them his name — the Camel is his horse turned to stone, the Boot the one he lost running. The Wishing Chair is a seat of columns, and it is worn smooth, not by the sea but by everyone who has stopped to sit in it before you.