Black Widow - Sacrifice (1970)
I got this from through our ever-reliable Anteater and it's good fun, a solid heavy prog album.
A few sources seem to be claiming it's heavy metal but there are far too many flutes; this comparison is obviously down to the cliche B-movie occultism - lyrics and themes that would dominate metal subgenres for decades to come.
There's not a lot of musical showmanship on offer here for a prog album, but plenty of Vox organ and the grooves are sufficiently stoned / the wails sufficiently proto-metal to keep you smiling. An interesting document, early Sabbath similarities aside! The artwork's creepier than the music though, it has to be said.