5. Antrim, Northern Ireland
The remarkable Giant’s Causeway is on the coast of Northern Ireland. It is the result of a volcanic eruption an eon ago – well, sixty million years, at least. The over forty thousand columns of stone are made of basalt, which essentially is cooled lava.
The distinctive feature is that the majority of the columns have a hexagonal shape and smooth tops. This allows you to walk on them! They progress down from a cliff and the formation continues into and beneath the sea.