This especially in remote locations! On the job sometimes when I would open up for the shift I would stop underground in one of the oldest tunnels that had been open since the mid 1800s and cut the ignition to sit for about a minute or two in complete darkness and/or silence. However, on some occasions that silence is disrupted by a thump of a small rock and then id turn on the lights and start prodding the roof. I think the most uncomfortable I have been is going to the tunnels that hadn't been rehabbed and hearing a jingle of keys or a chain knowing no one else was down there but our crew or when that sensor lights up red blaring and the air gets cold and then it stops. Talk about scary maybe paranormal. The superstitious among us and myself think it is the old mine manager that died down here when one of the tunnels collapsed a few decades back. Oddly enough we even have a saint mounted at one of the main portals above a wall of hard hats. I'd pray every morning I opened the shift and went down under.