About 30 miles (45 km) north of Rome there is one of the world’s most amazing feats of military engineering. The tunnels inside the mountain were built for Mussolini but were used by Field Marshal Kesselring as Nazi headquarters during the Battle for Rome. The Nazis had around a thousand troops living and working inside the bomb proof  mountain. The site was burned out by them when they fled north and anything of value was looted. Nowadays a local volunteer group gives guided tours around the complex.