I was one of them. It was pretty dicey - the tunnels and sewers were in major upheaval (this was shortly after the Earthquake). In one spot, the passage was completely blocked. Near the area we found the gun, there appeared to be a haunting, or ghost.
I’ve ain’t had reason to go back, so didn’t. I assume if the feds are doing major work there, they’d also work on the stuff below surface, if only for stability and sewage. Which I’d bet, if they did that, they set up some alert systems. (especially if they ran into a haunting experience!)