On February 28, 1995, the Denver International Airport opened its doors and its runways to the general public after falling over a year behind schedule and spending a reported $2 billion more than its original budget had dictated.

The massive new airport didn’t just take up lots of time and money—it also took up a lot of space: two decades later, it’s still the largest airport in the United States by area (53 square miles) with the longest public use runway available in the country (runway 16R/34L is 16,000 feet long—approximately three miles). DIA replaced Denver’s old Stapleton International Airport, which was plagued by problems (runways too close together, a general lack of space for necessary expansion), and its creation helped meet some basic needs that Stapleton simply couldn’t. Denver needed more room to serve the various airlines that had made—and wanted to make—the Mile High City a hub of operations, and DIA did just that.

That all sounds normal enough, right? A city needed a new airport, and it got one, even though it took a lot more money and time than originally planned, as so often happens with large-scale public works (although there is some debate as to who actually funded the airport, but we’ll get to that). But for the last 20 years, people have wondered if DIA—giant, expensive, strange DIA—is home to something far more sinister ... like a conspiracy. Or a lot of conspiracies.

1. The Runway Shape

Although one of the underlying themes of the various conspiracy theories regarding DIA holds that Stapleton was a fine airport and didn’t need to be replaced, there is one inarguable point: the runways at Stapleton were not smartly laid out. The parallel runways were too close together for safe landing in bad weather, which happened around 150 days a year and cut the number of arrivals an hour from 80 to 36. DIA doesn’t have the same problem, but it does have something far more nefarious: a shape that many people have noticed looks curiously like a swastika, at least from the air. Taken on its own, such a shape could be brushed off as being just a really terrible piece of planning, but combined with everything else, it all looks very odd indeed.

2. The Markings

The airport bears a series of “strange” markings on its floors that some people believe symbolize a new strain of hepatitis that could be used in biological warfare. In reality, most of the symbols are taken from Navajo language or are pulled from the periodic table of elements.

3. The Dedication Marker

There is one very weird marker that’s hard to ignore: a dedication marker and capstone that’s been placed over a time capsule (which supposedly includes a credit card, Colorado flag, and DIA opening day newspapers, among many other things) that is set to be opened in 2094. The symbols on the marker are associated with the Freemasons, a charitable organization that is often subject to their own conspiracy theories. The marker also mentions the “New World Airport Commission,” an organization that doesn’t actually exist (or does it? our brains are spinning!) but appears to be taking credit for building the entire airport. However, the contributors listed as part of the so-called NWAC, including an architecture firm and a metal company, do exist. And they just make buildings and metals. Well, probably.

4. and 5. The Tunnels and the Underground Bunker

The airport is home to a number of tunnels, including a tram that goes between concourses and a failed automated baggage system. That all sounds normal enough, but there is definitely something weird about that automated baggage system—mainly, that it cost a lot of money and then never actually worked. The system, which failed pretty spectacularly when it was first tested and just never got better, was one of the reasons for DIA's delayed opening. By 2005, most of the airport’s concourses had abandoned it totally, making both its bloated price and long delays feel like even more of a failure—or at least a really weird way to cover up the building of tunnels.

But where do the tunnels go? Perhaps to some kind of underground bunker? Most of the people who believe in the various conspiracy theories regarding DIA seem to think that the airport is actually the headquarters for something far nastier than just an airport—like the New World Order or our own American government. This idea might sound pretty wild—just because the place is big? just because of all that weird stuff in the airport?—but there is something very strange to back it up: buried buildings.

As the story goes, when DIA was first being built, five massive buildings were built somehow incorrectly. Instead of being blown up or otherwise dismantled, they were buried. Although theorists say that a construction worker ultimately blew the whistle on this very weird practice, finding his original testimony on the subject is almost impossible.

BONUS: The Horse Statue and the Weird Murals

Conspiracy theories aside, it’s hard to deny the weirdness of DIA’s unofficial mascot—a massive horse statue called “Blue Mustang” that has already killed at least one man. At 32 feet tall and 9000 pounds (it’s made out of fiberglass), “Blue Mustang” is huge and imposing, and its glowing red eyes don’t help matters. This thing is giant and really scary—and it killed the man who made it. Really. Artist Luis Jimenez died in 2006 when a piece of the sculpture’s head broke off and severed an artery in his leg.

Leo Tanguma’s two murals, which take up wide swathes of wallspace in DIA’s baggage claim, might have some nice names—they are called “Children of the World Dream of Peace” and “In Peace and Harmony with Nature,” respectively—but their actual content is terrifying. Death-masked soldiers stalk children with guns, animals are dead and kept under glass, and the entire world looks to have been destroyed. As if being at the airport isn’t bad enough.

To his credit, the narrative of Tanguma’s murals ends on a happy note—with all that peace and harmony stuff—and the artist himself has said, “I have children sleeping amid the debris of war and this warmonger is killing the dove of peace, but the kids are dreaming of something better in the future and their little dream goes behind the general and continues behind this group of people, and the kids are dreaming that [peace] will happen someday. See how the little dream becomes something really beautiful, that someday the nations of the world will abandon war and come together.” Still, the last place anyone wants to see depictions of death and destruction in an airport.