A fogou is an underground structure which is found in many Iron Age settlements in Cornwall. The purpose of a fogou is now unknown, and there is little evidence to suggest what it might have been. It has been conjectured that they were used as refuges or for food storage. Their central location in settlements and the work which evidently went into constructing them is indicative of their importance, which may have been religious. Fogous consist of a buried, stone slab-lined gallery.

The word derives from the Cornish ifócw, meaning a cave.

Fogous are known as souterrains elsewhere in the British Isles and in Brittany.

A notable example of an unspoiled fogou is to be found at Carn Euny in Cornwall.