Definitely not for the faint of heart, the city’s catacombs are filled with the remains of millions of Parisians whose bones line the narrow passages of this mazelike series of tunnels. In the 18th century, the Cimetière des Innocents, a centuries-old, overpacked cemetery near Les Halles, had become so foul and disease-ridden that it was finally declared a health hazard and closed. The bones of its occupants were transferred to this former quarry, which were later joined by those of other similarly pestilential Parisian cemeteries. In 1814, the quarry stopped accepting new lodgers, and the quarry inspector had a novel idea. Rather than leaving just a hodgepodge of random bones, he organized them in neat stacks and geometric designs, punctuating the 2km (1 1/4 miles) with sculptures and pithy sayings carved into the rock. The one at the entrance sets the tone: STOP—HERE IS THE EMPIRE OF DEATH. The visit will be fascinating for some, terrifying for others; not a good idea for claustrophobes or small children. The lighting is appropriately eerie, so you should bring a flashlight if you really want to see. Explanations are in English, French, and Spanish. It’s cool down here (around 12°C/54°F) and damp, so a jacket or sweatshirt and rubber-soled shoes are indispensable. Audioguides in English (5€) add interesting titbits of information to the visit. In recent years the attraction has become incredibly popular, so be prepared to queue or arrive 15 minutes before opening.