Airbnb has sparked mild controversy in Paris after offering curious travellers the chance to spend a night in the "world's largest grave".
The accommodation rental website says the winners of a Halloween-themed competition will become the first people to wake up alive in the catacombs underneath the city that hold the remains of more than six million people.
Opposition politicians on the Paris city council, meanwhile, have urged Mayor Anne Hidalgo not to forget a French law saying "respect due to the human body does not cease with death."
'Tableau of death'
But what exactly will the overnight guests encounter during their stay in the Paris catacombs?
Well, firstly, millions of bones arranged in what has been described as a "tableau of death" in high Romantic style.
Only a small part of the labyrinthine tunnels below Paris are open to the public, and visitors descend 20m (nearly 66ft) below ground to tour a 2km (1.2-mile) section of dark tunnels where the bones are kept.
They are greeted with the verse: "Halt, this is the realm of death."
It is the first of a number of inscriptions in the catacombs meant to give "pause for thought" to visitors.
The remains of more than six million people were gradually moved below ground in the late 18th and mid-19th Century as overcrowded graveyards in Paris were closed because of public health concerns. This included the belief that wine and milk was going bad because of the decomposition of bodies in the city.
The first graveyard to be closed was the Cimetiere des Innocents in 1786.
The catacombs are part of a huge network of tunnels in the bowels of the city. Limestone and gypsum from these quarries were mined beginning in Roman times to provide the stone from which Paris was built.
In 1774, the collapse of a chamber saw King Louis XVI order the reinforcement and mapping of the network, the vast majority of which has been closed to the public since 1955.
But the more than 250km of passageways officially off-limits are accessible through various hidden entrances around the city to those in the know - including through sewers, basements and metro tunnels.
They are home to an array of subterranean secrets. In 2004, police stumbled across a secret cinema complete with an electric-powered screen, bar and seating carved into the rock.
The underground network has also been known to host clandestine art shows, theatre performances, university hazing rituals and parties hosted by so-called "cataphiles"
This is the name given to Parisian explorers who secretly descend into the tunnels for fun.
AFP has reported that Airbnb paid up to 350,000 euros (£258,000) to rent the catacombs normally accessible to the public for a night.
The company says its two guests will be treated to a private underground concert and bedtime storytelling.
The house rules include not to "follow ghosts through the galleries".