Sparkfolk "bar"/social club intentionally built on top of a large boiler room (which serves some other purpose as well). Speakeasy-ish vibes, doesn't have a sign or anything, you just have to know it's there.

Built without the building owner's knowledge, but the foreman/managers/whatever gets a nominal cut, plus it just would have been wasted space anyway, a bit too warm to even use as storage for most things.