The exterior building in the 2nd drug trip where Sam entered was first discovered in 2020. It inspired the director to give it a real "Stephen King's Overlook Hotel" vibe. The location of that building remains exactly as it was the day it was shot and the day it was first discovered in 2020. It is a well maintained building in a well maintained area with no signs of life. It's intimidating exterior is exactly what the director was seeking out for the movie. The closer you get, the more you feel you are entering the belly of the beast.
Production started in October, 2021. Unfortunately, between the pandemic, China's covid zero tolerance policies, lockdowns, other obligated projects from the cast and crew, and protests, production wasn't able to finish until November 2022. One month worth of filming shot in a year.
There were certain scenes where the audio equipment failed during shooting. However, due to supply issues, new equipment for audio couldn't be delivered because of the pandemic. The director would spend hours finding sound bites to match the video footage. One example was the scene in the 2nd drug trip. In the interior scene when Sam was exploring the building, the entire sequence up until the ax had no audio. The director spent 30 minutes alone to come up with the 4 sound bites to combine for the beer bottle that Sam kicked.
Due to lockdowns in October of 2022, two scenes could not be shot and some other scenes couldn't be completed. Those scenes would've added more layers to the character of Ramse as a direct connection to the character of Dr. Casper Darling from the video game, Control. The lost scenes would've also been a direct connection between Ramses "Associates" and The Observers from the television show, Fringe.
Shooting took place entirely on location in Fushun City. It may be an obscure location, but it has a notable place in Chinese history. Fushun witnessed the rise and fall of the last Chinese dynasty, the Qing Dynasty (1636 - 1912). It was the birthplace of the first Qing Dynasty Emperor, Nurhachi. Emperor Nurhaci was a story element in the opening scene of the 1984 film, Indiana Jones and the Temple of Doom. Fushun was also the city where the last emperor, Pu Yi, was imprisoned as it was depicted in the 1987 film The Last Emperor.