Carn Euny is an archaeological site near Sancreed, on the Penwith peninsula in Cornwall, United Kingdom with considerable evidence of both Iron Age and post-Iron Age settlement. Excavations on this site have shown that there was activity at Carn Euny as early as the Neolithic period. There is evidence that shows that the first timber huts in this site were built around 200 BC, but by the first century before Christ, these timber huts had been replaced by stone huts. The remains of these stone huts are still visible today.
Carn Euny is best known for the well-preserved state of the large fogou, an underground passageway, which is more than 65 feet (20 metres) long. This fogou runs just below the surface of the ground and is roofed with massive stone slabs. Although the exact purpose of these fogous is still a mystery, possibilities include storage, habitation, or ritual. The site was abandoned late in the Roman period.