If you are looking for a historic and adventurous hike in the Argonne Forest, you can explore the Kaiser Tunnel near Lachalade. This tunnel was built by the German army during the First World War to allow the movement of troops and supplies without being detected by the enemy. The tunnel is approximately 350 meters long and has various facilities such as a hospital, kitchen and generator room. You can access the tunnel through the north entrance or the south entrance, both of which are classified as historical monuments. The tunnel has been closed to the public since 2012 for security reasons, but you can still admire its impressive structure and imagine the life of the soldiers who went through it. The Kaiser Tunnel is part of a network of other tunnels and trenches that you can also visit in the region.