When it comes to horror movies, ghosts and/or haunted houses are usually popular topics. Some ghost stories are just awful, while others are fantastic. Fortunately, The Haunting is part of the latter.
One of the things I love about classic horror films is that they (for the most part) rely on imagination to scare you, unlike today's horror films which are usually filled with gore. This film is scary in the psychological sense, which is what makes it so terrifying. An example: Nell (Jullie Harris) and Theo (Claire Bloom) are in their room when Nell hears noises outside of the bedroom door, causing Nell to grab Theo's hand. Nell starts screaming and wakes up Theo, who was asleep on the other side of the room and was obviously not the one holding her hand. There are many scenes like this one in The Haunting, but I found this one by far to be the most frightening.
Overall, The Haunting contains no blood or monsters, but it still remains to be utterly horrifying even forty-eight years after it's release. Don't skip this one.