A few years ago(OK decades ago), I was hiking with some friends in the Swiss Mountains. The weather was nice, the sun was bright and their was a cool breeze in the air. We stop from time to time to rest. At one of these stops, we placed our knapsacks on the grass and leaned across the steep boulders behind us. Usually mountain boulders are cold and slightly damp. This particular large rock was warm to the touch, dry and felt smooth. We looked closer at the boulder, and it was painted fiber glass that was covering something. We ran our hands on the boulder until we found the edge of the fiber glass sheet. We pulled it slightly from the rock and peeked in. There was a solid concrete wall inside the mountain face and an entrance through a fortified lead vault door. We heard stories before of the Swiss having hidden military airports and army bases deep inside their mountains, but this was the first time we ever saw something like that for real. My guess is it was a Nuclear Fallout Shelter.
Here are pictures of someone who has actually gone inside a Swiss fallout shelter.