The Guardians of Danville
The Mines date back prior to the founding of Danville in its current form, by Kurt Doofenshmirtz to when it was a copper mining town. The historical nature of the mining means that records of the mines themselves are poorly kept, and before any building construction in Danville, city legislation requires a Inator Corporation proxy to perform a ground survey, to ensure that the ground underneath is stable enough to take the building. Often, concrete reinforcement is required.
The primary entrance to the mines, along with a smelting plant, is within the Perryworks but the mines themselves run for up to 30 miles out from this point.
The mines have been officially abandoned for years, but the Inator Corporation is rumored to have repurposed some of these mines as deep labs in the sixties and seventies, hiding their work from Russian Satellites deep in the earth. If this is the case, who knows what is down there?