Famed for its thousands of interlocking hexagonal columns that rise vertically like steps, the Giant’s Causeway is a geological oddity that looks distinctly man-made.

In fact, the unusual formation was born of natural processes during the Paleogene (65-23 million years ago), when Northern Ireland was subject to powerful volcanic activity. During this period, molten basalt came into contact with chalk beds, forming a lava plateau. When the lava cooled quickly, the plateau contracted and cracked, forming 40,000 hexagonal columns of varying heights that look like giant stepping stones. The largest stand almost 36 feet tall.

According to legend, an Irish giant by the name of Fionn mac Cumhaill constructed the causeway himself so that he could skip over to Scotland to defeat his Scottish rival, Benandonner. Apparently, while in transit to Scotland, Fionn fell asleep, and Benandonner decided to cross the causeway to look for his competitor. To protect her slumbering husband, Fionn’s wife gathered him up and wrapped him up in cloth in order to camouflage him as their child. When Benandonner made it to Northern Ireland he saw the large infant and could only imagine how big Fionn must be. Frightened, Benandonner fled back to Scotland. But the causeway remained.

Although the phenomenon of basalt columns is relatively rare, there are a few dramatic examples of the rock formation found around the world, including Fingal’s Cave in Scotland, Los Prismas Basálticos in Mexico, and the Devil’s Postpile in California.