Deep beneath the streets of Paris, police are playing a game of cat and mouse with a band of explorers who have turned the city's underground tunnels and chambers, a 186-mile labyrinth of former quarries from which stone was extracted in Roman times and the Middle Ages to build the city, into their personal playground. The so-called cataphiles, equipped with waders, torches and rucksacks, drop in through manholes to explore disused medieval quarries and catacombs filled with human bones, spray graffiti and throw parties. The entrance of the carriers is kept secret. Down there, the temperature is a constant 15 degrees Celsius (59 degrees Fahrenheit) and the humidity 100 per cent. Visiting Paris underground is a very good way of rediscovering the history of the French capital. The Parisian resistance, during world war two, lead by Roll Tanguy, had its headquarters in a Bunker hidden in the quarries. A German bunker can be visited as well, most of the Nazi vestiges are gone now from the bunker but there are still warnings like "RAUCHEN VERBOTEN", and sealable metal doors that look like they belong on a U2 submarine... Let's start our journey in this illegal and secret world, welcome to Paris’s true belly (intestine?), the city of darkness under the city of lights.