The fogou at Carn Euny is one of the best-preserved and largest surviving fogous anywhere. It dates back to the Iron Age, around 200BC.
The underground passageway measures more than 65 feet (20 metres) long running just below the ground it is roofed with massive stone slabs. To one side of the fogou is a large circular chamber.
What fogous like this were used for is somewhat of a mystery. Possible uses include storage, habitation, or ritual.