Remember when lightning struck the Salt Lake City Mormon Temple a couple years ago, and the Angel Moroni fell off? Apparently, that's not the whole story; the whole temple nearly fell. They are now semi-secretly rebuilding it (they are calling it "renovations"), and the workers found a giant network of tunnels underneath the temple.
Start at 11:15 in this video: https://www.youtube.com/watch?v=YDf_ymNRk6E
LIved there a long time ago. When they rebuilt a good sized chunk of downtown it exposed a massive underground area very close to the temple. Didn't think much of it back then, but now that I know what I know now...
Home town for me. Lived there since 1952