I had the same answer from other girls in other places.

That was the mise-en-scène of the battle of Loos⁠—those mining towns behind the lines, then a maze of communication trenches entered from a place called Philosophe, leading up to the trench-lines beyond Vermelles, and running northward to Cambrin and Givenchy, opposite Hulluch, Haisnes, and La Bassée, where the enemy had his trenches and earthworks among the slag heaps, the pitheads, the corons and the cités , all broken by gunfire, and nowhere a sign of human life aboveground, in which many men were hidden.