What is the best horror film you have ever watched?

I wouldn’t call it a “horror film” as much as a supernatural thriller, perhaps, but nevertheless,
there’s something tremendously creepy and desperately sad about this one:

George C. Scott plays John Russell, a classical composer who loses his family in a horrific accident.
To cope with his grief, he rents a big, spooky house (but of course!) where he can spend his days in solitude and get some work done on his piano.

Needless to say, he’s not quite as alone in the house as he’d like to be.
Strange things keep happening in the shadows and someone (or something) seems very keen on getting his attention. The only question is: Why?

To say more would be spoiling it. Once you’ve seen it, the clue to the film is in its title.
But I will say that if I was John Russell in that house, I’d be out the door as soon as I heard the first noise. John, however, is seemingly fearless and has no problem with exploring dusty corridors and attics in the dark…