Theres a second city hidden beneath the streets of Paris where busy inhabitants and wide-eyed tourists walk.

This intriguing city consists of 300 kilometers of subterranean tunnels,  originally used as a quarry in the XVIII century. However, for a place that was once known as the Mines of Paris it has found itself a rather somber end.  

Due to the excessive epidemics and deaths that Paris suffered over the years, the mines started to be used as an impromptu cemetery. The authorities discretely moved the bodies below ground and the quarries quickly transformed into real catacombs. The bones have been accumulating for decades; and today they calculate that over 6 million peoples remains from different eras lay here to rest.

In the case that your next home swap takes you to Paris, the catacombs have been officially open to the public since the early19th century--a great find for the curious at heart!