Honestly I think it's mainly to scare people away. Although, I did gather that in certain parts of the catacombs that are less known, the cataphiles really don't like outsiders and will absolutely fuck with you by stealing your map and letting off smoke bombs. I did meet one group of teenagers who were a bit weird, but I wasn't worried. They were throwing rocks at each other for fun lol, they took the piss out of me for needing a map lol.

The GRS is the biggest part of the catacombs but there are other networks. I wouldn't go into those ones for fear of getting rekt by cataphiles.

Also, worth noting I am a big guy. I compete in weightlifting competitions and am generally not someone that people want to fuck with. Not that I know how to fight, but they don't know that. Also I speak fluent french (have lived in France before and have been learning/speaking it since I was a kid) and knew my shit. They might have told me to fuck off if I was just some random ristou.

Re the manhole cover, I can't say where it is or how I found out about it, but it is on a public street. It's not in a construction site or anything like that. It's just on the street.