Writing for Intelligent Life, Will Hunt describes a trip from one side of Paris to the other that was almost entirely underground in his article, “Going Souterrain.” Modern cities have huge underground infrastructure, and some are large enough to permit men to travel through, though this is dangerous and almost uniformly illegal. In a city as that also ancient, like Paris which has areas that were populated back in Roman times, that goes double.
There are two things in Hunt’s article that I find particularly interesting. First, underground portions of Paris are tourist attractions and have been for a long time. I would be such a tourist, but I realize I’m in a minority. Second, Paris has as subculture of cataphiles, people who enjoy spending time in the catacombs and other underground structures of that city. They hang out in popular places, party, and sometime explore.
I do not advocate that unprepared amateurs should trespass on private property or enter underground utility tunnels or sewers. As I mentioned, it is dangerous. I do recommend reading “Going Soutterain."