Some good ones already named. A few more:
The Hills Have Eyes (original)
Rosemary’s Baby
Fire Walk With Me
The Descent
The VVitch
I’m all about dread and terror, not just gore. These five plus the classics like The Exorcist, Texas Chainsaw Massacre, The Shining, The Thing, all fit that bill.
Edit: Several already mentioned Rosemary’s Baby and The Descent.
Surprised nobody has mentioned The VVitch. I found it pretty unsettling in that way you get the creeps from a movie. Great cast. Strong visuals. The religious paranoia and fallout amongst the children was almost disturbing. Based on folklore of colonial times.