Norwich has been mined for chalk and flints since at least the 12th century for building and agricultural purposes. Harford Hills, which is to the south of the city, was the last working mine in the area, and was still being worked into the 1930s.
What remains are a labyrinth of tunnels, some intersecting at different levels but typically with the same upturned flower pot profile. Soot staining from candles appears to be from its period as a mine, and some cleaner tunnels may be more recent based on the absence of soot staining. Bad air has been reported in some sections at certain times of the year.
It was reused during the Second World War as the Eaton Auxiliary Unit Patrol hide and some remains may date from that period including the corrugated steel tunnel entrance and old cooking equipment.
The surface quarry workings are now wooded over and are open to the public as the Danby Wood Nature Reserve. The mine entrance is understood to have been sealed.
For further information regarding the Eaton Patrol refer to Coleshill House.