Starting off we have the Cheyenne Mountain Complex. It is located in Colorado and has a deep history as a base of operations in the 1950’s during the cold war. It was at this time where the threat of soviet bombings were high, so proper action needed to be taken in order so that everything was safe, which is why it was built inside of an entire mountain.
While it may seem a bit overkill, it certainly gets the job done. Since then, its use has declined substantially, still being maintained by the Air Force but at a much lower function. It’s weird to see such a huge construction not being used much and it makes you wonder if it ever will be prominent again.