I used to fly to Denver a lot when Stapleton Airport was still active, it was awesome and so much closer to my accounts there in the city.
Getting to and from DIA especially in the winter is a trek, not my favorite airport by any stretch and now we see what was really going on. If I remember correctly there was also a connection to a Clinton acolyte Federico Peña
https://www.cpr.org/news/story/meet-federico-pe-who-helped-decide-where-dia-and-why-it-needed-train
The existence of DUMBs (Deep Underground Military Bases) has been discussed for many years in many forums, some a little whacky and some well sourced. There is enough information about them out there that I am not averse to the notion that there are lots of them in the US. A quick search came up with this link, for example:
https://www.intellihub.com/do-deep-underground-military-bases-exist/
There is lots more info out there for those who want to research and decide. I view it as interesting and something to be aware of.