The Montagnac family motto is the French translation of a famous H.P. Lovecraft's quote: "That is not dead which can eternal lie, and with strange aeons, even death may die."
The directors explained in Variety (Jun 24, 2021) that "the house was built on large grids and progressively plunged into a nine-meter deep water tank that was 20 meters wide." and "We couldn't leave the whole house in the water for days at a time because the decors would have been ruined, so we would immerse only parts of the house under water, and were shooting scenes floor by floor." and "It was a risky shoot -- having the actors and some of the crew go six-meter deep was very uncommon and difficult to insure. Maury and Bustillo were not allowed to go down there and were following the shoot across five or six monitors and four cameras."
The dive would have killed both divers. Here, the dive was 100 ft for approximately 60 min: according to Haldane's Decompression Model, breathing atmospheric air at this depth for that amount of time would require 97 minutes of decompression in the water (assuming the divers did not bring a portable hyperbaric chamber and oxygen). Ascending from 100 ft to the surface after 60 min, without stopping to decompress in the water column, would result in catastrophic decompression injuries (the "bends"). Furthermore, holding your breath upon ascent would result in an additional and devastating diving injuries (e.g., arterial and/or pulmonary gas embolism).
Blumhouse Productions and Epix acquired the film for North American distribution.
Takes place in Southern France.