Catacombs and tunnels: discover the heritage, safely

An underground heritage, a history worth knowing

Under Paris, former limestone quarries supplied the stone that built the city. At the end of the 18th century, bones from overcrowded cemeteries were moved there: that is the origin of the municipal ossuary known as the Paris catacombs. The Inspection générale des carrières, created in 1777, was founded to consolidate this subsoil, and it still watches over voids that threaten to collapse.

Elsewhere in France and around the world, the same kind of heritage exists: quarries, mushroom farms, wartime shelters, refuge tunnels, wine or cheese cellars. Every place has its own history and its own owner.

Access: what is open, and what is not

For the Paris catacombs, only the fitted-out ossuary route is open to visitors. Access to the quarries and underground galleries of Paris outside the route open to the public is forbidden and dangerous: risk of collapse, falls, asphyxiation or flooding, not to mention the liability of those who venture in. This ban is not something to work around.

To discover this world legally, favour official visits, museums, open heritage sites, guided visits by associations or local authorities, and supervised outings in quarries run for tourism. Ask the organiser whether phones and scanning are allowed, and follow their rules.

If you are unsure whether a place is open, assume it is not and ask. A local heritage association, a tourist office or the town hall can usually tell you which underground sites welcome visitors and under what conditions.

What Lidark can bring within an authorised framework

If you are visiting, or in charge of an underground site with its owner’s agreement, a survey helps keep a record of the place:

• a dated 3D model of a cellar, tunnel, crypt or chamber, for the archives;
• a plan and an altitude profile, useful for a promotion project or a diagnosis;
• landmarks (shaft, inscriptions, danger) visible on the minimap and in 3D;
• PLY or OBJ export for work in MeshLab, CloudCompare or Blender.

Safety first

An old tunnel is a risky environment: unstable ceilings, waterlogged ground, low-oxygen air, complete darkness, no network to call for help. An authorised visit is prepared. Plan two light sources independent of the phone, a power bank, good shoes and a helmet if the organiser requires one. Tell someone your return time.

Lidark replaces neither a guide, nor a rope, nor a prior reconnaissance. It is designed to help you keep the thread of the path in a place where you have the right to be. Read finding your way with no GPS for the basic practices.

Respect the place

An underground site is quickly destroyed: a moved stone, a bone taken as a souvenir, an inscription wiped, and a testimony vanishes. Take nothing, mark nothing, do not light fragile walls for long if the organiser advises against it, and leave every spot as you found it. A 3D model is an excellent way to share a place without harming it, provided you have permission to survey it.

If you work with a site manager, agree beforehand on what may be recorded and who may see it. Some places restrict photography or publication for conservation or privacy reasons, and a 3D model of a crypt or a cellar can reveal as much as a photograph. Ask first, credit the managers when you share, and keep the data on the device until you have their go-ahead.

Going further

For professional uses of an underground survey, see the guide to quarries. For exploration in authorised places, see urbex. For the technology, see the iPhone LiDAR scan. And for any question: support or [email protected].