Imagine traveling down a stone passage into a dark series of tunnels, many with entrance gates made of wrought iron, which contain the remains of 6 million people. Welcome to the Paris Catacombs, a massive grave right under Paris streets (including homes and other buildings).
The situation begin in the 1200s when churches struggled to meet the demand of Christians wanting to be buried in consecrated ground. Most of the churches were located within Paris city limits but at the time no one stopped to consider how large the burial grounds would become. In time, the mass graves became overcrowded. Churches then started to bury remains one on top of the other. This solution contributed to a number of health risks including decaying remains being found in the drinking water!
The Paris government was in the process of finding and mapping long abandoned query mines which ran underneath the city. A police officer came up with the idea of filling the mines with the remains of the overcrowded cemeteries. Moving of human remains began in 1786 and continued for two years before it was completed.
The bones are created in an artistic fashion, with walls made out of skulls and femur bones arranged in heart shapes. One circular room has a column of human bones.
The Catacombs are opened to the public.