Hidden in Colorado Springs is one of the most secure bases in the US – the Cheyenne Mountain Complex.
Some hope the secretive entrance would replicate the iconic 'stargate' allowing instant travel to other galaxies from the hit sci-fi series Stargate.
However, the Cheyenne Mountain Complex, made operational in 1966, is in fact a military installation and nuclear bunker – located in Colorado at the Cheyenne Mountain Air Force Station.
The Colorado mountain is about 9,500ft high, and the tunnel entrance to the complex is about 2,000ft from the top.
Forces News has taken a look at what is inside the restricted-access US base, as seen in the video above.