In which English county is the site of the prehistoric flint mines known as Grimes Graves?

Grime's Graves is a large Neolithic flint mining complex in Norfolk, England. It lies 8 km (5.0 mi) north east from Brandon, Suffolk in the East of England. It was worked between c. 3000 and c. 1900 BC, although production may have continued well into the Bronze and Iron Ages (and later) owing to the low cost of flint compared with metals. Flint was much in demand for making polished stone axes in the Neolithic period. Much later, when flint had been replaced by metal tools, flint nodules were in demand for other uses, such as for building and as strikers for muskets.

The scheduled monument extends over an area of some 37 ha (91 acres) and consists of at least 433 shafts dug into the natural chalk to reach seams of flint. The largest shafts are more than 14 m (46 ft) deep and 12 m (39 ft) in diameter at the surface. It has been calculated that more than 2,000 tonnes of chalk had to be removed from the larger shafts, taking 20 men around five months, before stone of sufficient quality was reached. An upper 'topstone' and middle 'wallstone' seam of flint was dug through on the way to the deeper third 'floorstone' seam which most interested the miners. The site is managed by English Heritage and can be visited.