"Ladies and gentlemen, welcome to my Underground Lair..."
— Doctor Evil, Austin Powers
Greg: What is it with you guys and your freaking lairs? Do you think you're a dragon of something? Do you just secretly dream of spending your days sitting on a pile of treasure?
"I'm kinda sad, though. All these underground tunnels and lasers, but instead of having a rave we're using them for evil.
Hobbes: It's a lair! What is it with bad guys and lairs? Can't they just live in houses?
Socrates: Imagine a super villain living in a studio apartment in southeast central L.A. I wonder if they could afford the rent.
Notice how all these passages are sloping downwards! We are now going underground! All the most important rooms in my factory are deep down below the surface! There wouldn't be nearly enough space for them up on top! These rooms we are going to see are enormous! They're larger than football fields! No building in the world would be big enough to house them! But down here, underneath the ground, I've got all the space I want. There's no limit - so long as I hollow it out.
—Willy Wonka attempts to justify this trope.