I travelled around Switzerland by car many years ago. I noticed there were military trucks driving around all the time, but I never saw a military base. I also noticed there were many iron entrance doors in the side of the mountains on the roads with no apparent purpose. Then one day, I saw one of these doors opened with 2 guards standing out front as a military truck drove into it. Finally, I figured out these must…
https://upload.wikimedia.org/wikipedia/commons/b/bc/Gotthard...
From here you can see three really small parts of a Bunker/Fortress (a supermassive one, probably the biggest in switzerland) ~quite clear.