Tucked away in majestic Thetford Forest there’s a mysterious lunar landscape, as if a huge meteorite shower once pounded the Breckland heath. Precisely 433 craters spread over 90 acres, strange hollows that seem hammered by a Norse god. No, not the mighty Thor but his pal, Odin. Odin’s Anglo-Saxon name is Woden, nicknamed Grim. Hence, Grimes Graves.

So was this fascinating place really created by ancient gods? The truth is, this heritage site was a Neolithic flint mine, made by humans some 5,000 years ago. In the days before our ancestors forged metal, super sharp flints were ‘knapped’ into tools, weapons and ceremonial objects. At Grimes Graves miners dug vertical shafts up to 13 metres deep and excavated narrow galleries which they crawled along, gouging out flint with pickaxes made from deer antlers. But what else might have taken place down in those dark tunnels? Animal bones and even a human skull have been found, along with evidence of underground fires, suggesting this was once a place of sacred rituals. And it’s likely what you see today is only part of the subterranean labyrinth which probably extended far under the pine forest.

Visitors can descend 9 metres (30 ft) by ladder into an excavated shaft to see the jet-black flint, which is itself another layer of deep time. Flint is the fossilised remains of soft-bodied sponges once swimming in the warm Cretaceous seas which, millions of years ago, covered the very place you now stand.