In the deeper parts of the facility, at random times, fog will suddenly condense around the players and a loud high pitched ringing noise will play in their heads. This fog prevents them from seeing 10 meters in front of them with normal eyesight. The fog will clear up after a minute, and the player is otherwise safe.
In the more abstract locations, doors, hallways, or even entire rooms can disappear and be replaced with something else entirely. This only happens when no one is looking.
Players may have their vision obscured by something, such as blinking or smoke, only to see they're in an entirely different location.
Screaming has been heard in the Deepwell Facility, despite the Authority only ever sending 1 person or crew of persons at a time.
Certain people have been able to see markings on the walls of unknown occult symbolize. These are invisible to everyone else and can cause a loss of sanity in a person. Some symbols can cause hazardous effects, such as causing observers to caught up blood, have seizures, cause them to permanently stare at the symbols unless forcibly removed, cause their the synapses in their brain to catch fire, mind control them, or even simply cause death after minute of staring. Those who observe the more dangerous symbols rapidly go under a drastic personality change, becoming more erratic, irritable, terrified, or religiously devote to a claimed higher power.