St Keverne local history website has this interesting page by Margaret Hunt,
Amazing pictures and details of the excavation carried out Oct 2003......
The fogou tunnel, when excavated, revealed a magnificent structure with walling up to 1.5 m high and a scatter of huge lintel stones lying haphazardly just above the floor level. A possible human tooth was found lying near the floor surface next to pieces of black burnished ware pottery.