The true event that the movie is based on happened in Georgia, where this film is made and filmmakers are from. 4 friends were in the sauna, one left for the toilet, locking his friends in - exactly as it is shown in the movie. He never came back, and when he woke up he didn't remember that he left them in the sauna, and started to search for them elsewhere. Fortunately no one died since they managed to turn the heater off, but they had to spend over 10 hours in the decreasing heat, until they were found.