The Butte de Vauquois, an hour's drive west of Verdun, is the most extraordinary preserved sector of the entire Western Front. A small hilltop village before 1914, it was contested by hand-to-hand fighting and then by underground mine warfare so intense that the village itself disappeared. The hill remains a moonscape of vast craters, with German and French trenches now stabilised and open to visitors.
A volunteer association leads guided visits down into the surviving tunnels (booking required); the surface walk is free and self-guided, with information panels along a marked path. A small but well-presented museum at the foot of the hill explains the mine war. Allow half a day, and bring sturdy shoes — the path is muddy in wet weather.