Based on the short story Out of the Aeons by American writers H. P. Lovecraft and Hazel Heald, first published in 1935 in Weird Tales magazine.
There is a Cool S graffiti sign on the bathroom wall.
Because the movie was filmed during the Covid-19 pandemic, J.K. Simmons (Ghat) was never on set. He and Ryan Kwanten (Wes) rehearsed several times on video calls. Once they each had a sense of how to react to each other's lines and deliver their own, they were able to record separately.