This small ridge, which is 200m high, 30km long and 8km wide, has been a strategic point on the north European road since Ancient times. Caesar took on hordes of Gauls here. But it was above all the scene of extremely bloody combat in the First World War. Eight historic sites are dotted along the route, including the famous Dragon's Lair, a cave network from which stone was extracted to build the Abbaye de Vauclair (1134). The network has since been turned into a Museum of Remembrance documenting the suffering of the soldiers of the First World War.