Shortly after Disneyland opened, Walt Disney realized that it looked kind of odd when he had cowboys walking through Tomorrowland and astronauts walking through a Renaissance fair. When it came time to build Disney World, he wasn't having none of that shit. Before any of the park pavement went down and before any of the rides went up, Disney had a series of tunnels, dressing rooms and secret doors built first. And everything else went on top.
Kingdom Keepers Wiki
"Disney World is finally complete, the culmination of my life's work oh shit we forgot to build air holes!"
But the fact that you're walking on top of a secret city isn't even the sinister part. If you've ever been to a Disney park, one thing will stand out: It's clean. Thousands and thousands of people are all around you, most of them kids, and there is zero trash on the ground. No sticky gum residue, no used condoms or old panties to be seen anywhere. Everything is clean. Have you guessed why? Because people are popping up out of the ground to clean that shit up, like mole people, quickly disappearing back into their subterranean kingdom with you none the wiser. The only way to figure out where they're coming from is to casually dump a purse full of fingernail clippings on the ground and stand aside to watch what happens.