"[O]ne of those places that everyone wants to see and no one wants to see again" is how Nadar described the catacombs. The Paris catacombs were former underground quarries that were refitted to house skeletons. Nadar ventured into them to create an unprecedented series of photographs illuminated by flashlight. He used a magnesium lamp, visible in the lower right corner of the image.
Six or seven million skeletons were interred in the catacombs; in this photograph, seemingly every one is accounted for. Only sixteen carefully stacked protruding skulls on the wall are clearly distinguishable at left, yet they are all that is needed to indicate what the blackened squares in the distance represent.
Around the time that Nadar made this series of a hundred photographs in the catacombs, two of his beloved friends passed away. The photographer may have been exploring his own mortality when he embarked upon this series, but it was also a fashionable pursuit to descend into these macabre depths. In mid-nineteenth century Paris, there were four annual visiting days for the catacombs, at which time they were filled with curious onlookers.