The following photographs were taken in the passages under Paris:
By the late 18th century, all the cemeteries were full. With disease running rampant through Europe, it was decided that the old limestone quarries would be converted into ossuaries for more hygienic mass burial. This continued until 1860. At the beginning of the 19th century, the Catacombs opened to the public.
(A black line is painted on the ceiling to keep visitors from getting disorientated.)
Something they do not mention at the entrance is that the passages are wet. The ceiling drips constantly, making the air heavy, the path muddy, and the bones glisten.
Claustrophobics, beware! The Catacombs are 20 meters below ground and the ceilings are low. This experience is not for the faint of heart, but well worth the risk.
The Catacombs are located across from metro Denfer-Rochereau. They are open from Tuesday to Sunday, 10h-17h. The walk is a total of 2km, and takes approximately 45 minutes.