The underground super-base at Cheyenne Mountain (science video).
Here’s a 50-minute-long documentary about the US underground super base at Cheyenne Mountain.
Of course, in fiction, said base served as the central command for the secret Stargate program. But in reality, the massive bunker monitors the skies for unidentified aircraft, missile launches, space objects, and even falling space debris.
Some say UFOs, also, that might be a disclosure too far for you!