All the walls of the start room have morse code on them. The text by the entrance may be saying Vite, which is the French word for quickly. The 11 minute wrist timer seems to confirm this.
The last scene was shot at Ouzoud Waterfalls in Morocco.
Director Mathieu Turi has developed a specialism and passion for intriguing films set in frightening enclosed spaces.
Bérénice Marlohe was originally set to play the main part, but had to drop out before shooting began.