Carn Euny (from Cornish: Karn Uni)[1] is an archaeological site near Sancreed, on the Penwith peninsula in Cornwall, United Kingdom.

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.

Traces of human activity in Carn Euny have been detected from the early Neolithic period.

[5] The most important structure of the site is the fogou (Ogo being Cornish for cave),[5] a man-made underground passage which is covered with massive stone slabs.

The fogou at Carn Euny is in particularly good condition and consists of a 20 m long corridor, with a side passage that leads to a round stone chamber with a collapsed roof, and a small tunnel which may be a second entrance.

[6] At this time the people of Carn Euny lived from agriculture, livestock, trade, and perhaps tin mining.

Between 1863 and 1868, the antiquarian William Copeland Borlase examined the archaeological site and exposed the fogou.