Top 10 Cities for Urban Exploration

Far below the circus-tent canopies of Denver International Airport lies a network of tunnels -- restricted to all but a few people. Gary Conner/Photolibrary/Getty Images

Big draw: The airport (That's right, the airport.)

Denver International Airport (DIA) is more than simply one of the largest and busiest in the world. It's also the subject of some of the most bizarre conspiracy theories of modern times.

There are tunnels there -- extensive networks running beneath the airport -- where few people are allowed entry.

Aside from baggage handlers, that is. These tunnels were built as the main routes of a state-of-the-art baggage-handling system designed specifically for DIA, which failed immediately and miserably, and currently host the working, low-tech system that gets bags from one end of the sprawling airport to the other [source: Johnson].

Some conspiracy theorists believe the airport was built as a decoy -- a sort of key to the unfolding of the end of days or a secure location for the righteous when that time comes. Secret governments and the Freemasons play into the theories, too.

Those tunnels are essential to the story, but there's more: DIA was (somewhat controversially) constructed in what used to be the true middle of nowhere, far from the city center and general populace; inside, commissioned murals depict apparently apocalyptic messages; and an inscription in one terminal wall seems to loosely reference the New World Order, a famous conspiracy theory involving a one-world government [source: Mahers].

Access to the tunnels is restricted, of course; but most of the other evidence is open to the ticket-holding public.

More to explore:

  • Abandoned weapons silos, military airfields and nuclear burial grounds.
  • Abandoned air-traffic-control tower at what used to be Stapleton Airport, the only remaining evidence of DIA's predecessor.

Then, eastward ...