There are so many rumors swirling around about what's under Colorado.

Many residents have heard about a secret military city under Denver International Airport, even a government project on aliens down there.

Coloradans have heard about what it’s like inside the most famous underground military base in the world: Cheyenne Mountain.

There might be whisperings about tunnels under the Colorado State Capitol, used back in the day for lawmakers to escape gunslingers or to sneak prostitutes into the building.

And who can forget about a bunch of old missile silos supposedly scattered around the state?

9NEWS decided to put the rumors to rest by visiting these places and finding out what really happens Under Colorado.

On Monday, 9NEWS took viewers inside Cheyenne Mountain. On Tuesday, 9NEWS went underneath the Colorado State Capitol building. On Wednesday, 9NEWS answered the most questioned underground space in Colorado: Denver International Airport.