The parent may have more direct insight, but the article does discuss the rules: "The rules were few, and clear. Respect the past of the catacombs. Take out what you take in. Resources are to be shared, even with strangers. No selling and no buying: barter exchange or gifting are the only acceptable modes of transaction. Help is to be given wherever necessary. Create with care—and do not destroy."

At least the person who introduced me told me one should be personally introduced - so I will respect it and leave it at that (it's nothing weird or complicated though and I wouldn't be surprised if rulesets have mutated and forked over time and subgroups). If you are ever in Paris and interested, feel free to reach out :)

I didn't actually read the article, but from what I heard the catacombs used to be a lot less safe. I've been told that in the 90s it would be a very bad idea to venture down as one or a small group of women without significant risk for personal safety. Some of the rules definitely come from just being able to preserve the space and experience, but I would guess that some of the social codes also come from enforcing a safer space.