Much has been written about the strangeness surrounding the Denver International Airport so I'm not going to go into that. Instead I'll provide a link to an article on the Mystery Surrounding Denver International Airport. No, in this post I'm going to give my ideas on what I think could be underneath DIA.
I think that there's something strange underneath the airport and I think that it is perhaps a continuity of government facility. In the event of catastrophe, the top members of the United States government would be moved to a COG facility in order to maintain some government in the face of disaster. COG facilities aren't that unusual in themselves, but all of the New World Order imagery in the above airport makes it seem a little more sinister.
I think that the airport was built where it was built because of it's relative remoteness to Denver, or anything else for that matter. In a widespread disaster, the government officials (or the NWO, Illuminati, etc.) could fly into DIA from anywhere in the world and then go immediately to the bunkers deep below. I've also heard that Denver (and Colorado for that matter) sits on a very resilient portion of the Earth's crust. The airport (or rather, the facility beneath it) is thus isolated and stable, protecting it from man-made as well as natural disasters.
I do not think that it is a secret research facility. My reasoning for this is that there are too many civilians buzzing around the place all the time. Having an international airport makes sense if you have survival bunkers underneath, but it really would serve no purpose for a secret research facility other than to perhaps hide it in plain sight. If that's the case though, why bother building the airport at all? Everything is already hidden underground. All of the imagery and the peculiar circumstances surrounding the construction have only served to bring more scrutiny upon DIA as well.
I think the bigger question here is why build the facility at all? There are perfectly good COG facilities already in existence. Why the need to build a new one under such strange circumstances and in that particular location? Does the government (or the New World Order) know something about the future that we don't? Something to think about.