I've always loved the Denver Airport conspiracy theory - that it is actually the secret headquarters of the illuminati or other organisations. It was $2bn over budget and has tunnels under it, which have led people to claim there are also secret bunkers under the airport. It also has a few bizarre pieces of art within it.
I think it's just an airport with ugly aesthetic choices but I love that people think of all the places a global secret society would base itself, they'd pick Denver Airport.
Apparently there are 6 underground levels at the airport - but they're used to run an airport. And the tunnels were for a failed automated baggage transport system. The art is just art.