Deep under the streets of Paris, the tunnels, chambers and galleries of the catacombs run in all directions, some of them filled with the skeletons of the dead who were displaced in the eighteenth century from the overflowing cemeteries of Paris and moved here, their bones stacked six feet high and six feet deep along the walls. During World War II, the chambers and tunnels were used by the French Resistance and also by the Nazis. These days, tourists queue peacefully to totter down the delicate, steep, spindly steps into the underworld darkness, nervously following the guides through what feels like miles of tunnels. The mystery of the dripping noise is solved when you come back up into the sunlight to find your clothes streaked with the dissolving lime of the underworld.