The National Geographic states "Paris has a deeper and stranger connection to its underground than almost any city, and that underground is one of the richest." And there is a good reason for saying this. Paris has one of the oldest and densest subway and sewer networks in the world. While Paris is famous for its "catacombs" or "ossuaries" with an impressive 6 million people buried in them, that is only the start.

The labyrinth of tunnels running under Paris is truly mindboggling. There are spaces of just about all kinds one can think of - like crypts, bank vaults, canals, wine cellars, and miles upon miles of old limestone quarries. It reminds one of London that is rumored to have the largest secret tunnel network in the world - a tunnel network that does not include quarries.

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The Limestone Quarries

These limestone quarries form an intricate web under much of the southern parts of the city. Many of the stones in the city that one sees today, come from underneath the city. Into the 19th century, miners were quarrying for stones under this magnificent city. After they finished quarrying and as they were abandoned, these quarries have found many uses:

  • Farming: As Many As A Hundred Tons of Mushrooms Where Being Grow A Year A one Point
  • French Resistance: During WW2 French Resistance Fighters Hid In Some of Them
  • Bunkers: German During The War Built Bunkers In Some Of Them
  • Cataphiles: Today These Are The People Who Love The Paris Underground And Roam About In Them
  • Ossuaries: 6 Million French Have Been Buried In Them

Back in the day, these quarries were actually outside of the city proper. They were in semi-rural areas like Monmarte and Montparnasse. But the city grew and grew, and now these outskirts are very much within the city itself. Today the French Inspection Générale des Carrières or the IGC has the job of making sure Paris doesn't collapse in the quarries that so riddle its foundations.

Related: What You Need To Know About The Abandoned Speakeasy Tunnels Of Los Angeles

It's Illegal To Enter The Quarries

It has been illegal to enter these quarries since 1955. But famously the people of Paris have a rebellious streak and there are many (especially young people) who love to explore this underground world. For the cataphiles, the tunnels are a place to party, do drugs, stage performances, and enjoy the freedom of being somewhere long forgotten.

While it is forbidden to enter the mines. One can take tours of the ossuaries (or Paris catacombs) - these are short walks along lit walkways. It is so eerily to think that these Paris ossuaries are the final resting place of 6 million people and that one can actually visit them. But the vast bulk of the underground is off-limits.

  • Ossuary: 1.1 Miles or 1.7 Kilometers Of the Tunnels Have Been Used As An Underground Ossuary
  • Total Length: 186 Miles or 300 Kilometers of Tunnels And Disused Quarries Lay Under Paris

Many of these underground secrets - are just that, secrets. New discoveries are occurring regularly (like a gallery found underneath the Bois de Vincennes - one of Paris's largest parks). The extensive tunneling under Paris does make it somewhat at risk of sinkholes.

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Chemin de fer de Petite Ceinture

It's not just the quarries under Paris. Like London, the city also has abandoned railway lines - the Chemin de fer de Petite Ceinture (meaning the "smaller belt railway"). It was built as a way to supply the city's fortification walls and to connect with Paris' major rail-company stations.

It was built around 1851 and formed an arc surrounding the northern two-thirds of Paris and then a full circle when the last segment was completed in 1867.

  • Built: In The Mid 1800s
  • Closed: Closed To Passengers In 1934 and to Freight Line in The 1980s

Some of the sections have been repurposed but by the RER trains and some of the tunnels are sealed. but much of the old train line can still be discovered.

Related: Are There Really Tunnels Under New York City? This Is What We Know

Visit The Sewers Of Paris

While foul-smelling the sewers of Paris are also a very interesting part of the city's underground history. For this visit the Musée des Égouts or Museum of the Sewers of Paris. Walking down the museum's long and dark passages, visitors discover the history of the city's sewage system.

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It was during the First French Empire that the first covered sewage system was developed and in 1878 a double water distribution network sewage system over 372 miles long was introduced. Those who are fans of Victor Hugo's novel, Les Miserables, will learn how the sewers are portrayed extremely well.

  • 1 May - 30 September: Saturday - Wednesday: 11 am - 5 pm
  • 1 October - 30 April: Saturday - Wednesday: 11 am - 4 pm
  • Adults: € 4.40 (US$ 5.10)
  • Students: € 3.60 (US$ 4.20)

Next: This Is How You Can See The Roman Catacombs While You're In Rome