Fort de Douaumont in Douaumont-Vaux

You're standing at Fort Douaumont, on some of the highest ground around Verdun. Take a look around you. The land is still full of pits and bumps. Those are the scars of shells from the First World War. You barely see the fort as a building. It's tucked away under earth and concrete, about four hundred metres long. On the roof you can still spot steel gun turrets. They could rise up to fire and then sink straight back down.