I recently completed an internship in Trieste, Italy, the highlight of which was a day hike around the Tre Cime Nature Park in the Dolomites. On top of the incredible geology, the park features relics of the World War 1 front between Austria and Italy, such as the pictured trench and cave dug into the carbonate rocks. Besides tunnels, other war uses of the geology included the use of explosions to trigger fatal rock slides. I can't imagine fighting and hauling heavy equipment across (and up!) this rugged terrain.
• Geology of the Dolomites and WWI
• The Front at Tre Cime
• Geologists During WWI