 The approach to the salle du drapeau, the room of the flag, is the only time I feel real fear in the Parisian catacombs. It's early evening in the upper city by the time we get close to the room. Down in the invisible city, we are heading northwest along a tunnel with no side turnings, the ceiling of which is dropping steadily lower. I walk with bent neck and with hunched shoulders. Then I have to lean at the waist and then at last I have to drop to my knees and can only crawl forwards.