I'm neither old enough to have seen this sort of horror at the time (barely born, in fact) nor a real horror fan, but this came up late on BBC2.
The opening scene is nicely weird enough, with various symbols of witchcraft, with various symbols in sorts of colourful panto vignettes and then soon settles into normal life, old cars, Britishness and all that.
Looking for his disappeared brother, Robert Manning (a fairly ordinary, nice Mark Eden) drives off to this lodge, from where his brother's last letter was addressed from. On the way up, he is told that the village in question is holding an anniversary witchcraft celebration and finds cars of men chasing a girl running through the woods.
Reaching the Lodge, the owner, one J D Morley (Peter Cushing, no less) naturally denies any knowledge but offers him a room for the night. As one (naturally) does, in a big, strange old house, where there was a party that involved painting young lady's breasts (and similar!), Manning accepts. A joke with one young seductress about 'the sort of old house from the movies, where Boris Karloff appears' is nicely tongue-in- cheek, as the other big star here, is indeed, Karloff himself.
He plays a wheelchair-bound professor, who's hobby is collecting instruments of torture. And, of course there's a dodgy chauffeur who goes around shooting at things in the woods (including 'our' man) and who so happens to be mute and an even stranger caretaker. Them there's loads of kaleidoscopic hallucinatory nightmares, with electronically distorted sound FX that our Robert suffers, which are interesting, at least. Then he toddles off, sleepwalking down to the local graveyard.
It's all hoary nonsense, of course, but whilst a bit dated, there's enough interesting characters played by interesting - and/or sexy people, if you get my drift, for the film to remain entertaining and enjoyable.
I'd give the actual film 5/10 for its real merit and maybe 7 for the other, entertainment aspects, as I've outlined. I don't think many fans of this genre would be too disappointed either and for them it's definitely worth checking out.