Why is Denver Airport so big? How big is it, is it bigger than San Francisco, what are the 'hidden bunkers' and 'illuminati' conspiracy theories

Located roughly 20 miles from downtown Denver, the airport has dealt with its fair share of rumours since it was built. From the beginning, there have been theories about secret tunnels, clues regarding secret societies, and horrifying harbingers of doom "hidden" in public artwork around the popular hub.

Airport officials have also fuelled these wild ideas about secret Illuminati bunkers, underground tunnels, and links to aliens in marketing campaigns. At the airport you may even see signs with giant lizards dressed in construction gear.

A 32-foot fiberglass horse statue outside of the airport has also garnered conspiracies. Known locally as "Blucifer," the blue "Mustang" was made by artist Luis Jiménez.

Some say it is evil, pointing to the horse's glowing red eyes. But in reality Jiménez incorporated the effect with red LED floodlights as an homage to his father, who ran a neon sign shop during his formative years as an artist.

Jiménez died in 2006, two years before the project's end after a piece of the 9,000-pound sculpture had fallen on him and severed an artery in his leg. Since then, people have concocted all sorts of wild theories about the horse's true purpose — some even believe its eyes didn’t start glowing red until after its creator had died.

There are also theories about the many unmarked buildings and underground areas that have been discovered throughout the premises. According to the Mental Floss this conspiracy theory likely stemmed from a time capsule that was buried on the grounds, set to be reopened in 2094. It bears symbols related to the Freemasons, which has ties to the Illuminati - a secret society that dates back to 18th-century Europe. According to National Geographic, the group was known for its desire to reshape society by any means necessary, and its founder, Adam Weishaupt, is even thought by some to have brought about the French Revolution.

There are two reasons this rumour has had so much staying power over the years. First, the airport ended up costing a lot more than what was originally projected and second, it took much longer to build than expected. Conspiracy theorists believe Illuminati money was used to finish the job in exchange for secret access to the property.

There is a large network of underground tunnels, a train that runs between concourses, and a long-defunct automated baggage system, under the airport. The conspiracy is that the tunnels contain underground bunkers — possibly built by or even hiding lizard people or alien lifeforms — that will serve as a safe place for the world's elite during the apocalypse.

The airport itself operates on 53 square miles (34,000 acres, or 137.8 square kilometers) of land. That means the airport’s area is twice the size of Manhattan, and larger than the city boundaries of Boston, Miami or San Francisco.

In terms of airports, Hartsfield-Jackson Atlanta, Chicago O’Hare, Los Angeles International and Dallas Fort Worth could collectively fit into the airport’s expansive property. In fact Denver International Airport occupies more land area than San Francisco.