I found this article about a "newly" discovered Parisian underworld that exists below the streets. It is an eerie testament to thrill seekers today, though not exactly unheard of. While I was in Scotland, we went on a tour of "Mary King's Close." It was a tour of the streets under the main street of Edinburgh. Mary King lived in a corner unit and was one of the most famous residents in this terrifying existence. It was unbelievable - that people lived without sunlight and survived in the dank, squalid conditions. While it is surprising that anyone would want to repeat the experience, apparently the French have a yen for it. Go figure.