'A folk horror, wrapped in an archive film...'
A film like this lives or dies on its marketing. The above quote is how it's described on the BFI website, and it's this description that made me want to watch it; I had seen it available on iPlayer a while ago now, but I thought then that it was just some boring ass nature documentary so I passed on it, but now that I know it was meant to be a horror, I enjoyed it a lot more.
That's the power of expectations when going to watch a film: what you expect will determine how good you think it is.
And now I should talk about how fucking this is, but it defies explanation. To get the best experience, you have to gone in blind, so do that. Just watch it.
And the music is really fucking good too.