40,000 hexagonal stone columns look too perfect to be natural — but are

The Giant's Causeway on Northern Ireland's coast is a mass of roughly 40,000 interlocking basalt columns, most with hexagonal cross-sections, formed when a massive lava flow cooled and cracked into regular columns around 60 million years ago. Local legend credits the giant Finn McCool with building it as a path to Scotland; the geology is less romantic but nearly as striking. It became Northern Ireland's first UNESCO World Heritage Site in 1986.

— Wikipedia contributors, Giant's Causeway — County Antrim, Northern Ireland