In 1973, Black Sabbath were riding high on the success of theiralbum and mammoth tour of the U.S., Australia and Europe.

But when it came time to work on the Vol. IV follow up album, guitarist Tony Iommi, bassist Geezer Butler, drummer Bill Ward and vocalist Ozzy Osbourne found the writing well had simply run dry.

Despite trying to duplicate the surroundings and good times they had when writing Vol. IV - renting a house in Bel Air, snorting up bagfuls of cocaine and using LA's Record Plant Studios - they just couldn't replicate that magic in the summer of 1973. The drugs were taking a toll and Iommi, the guy everybody was waiting on to come up with the songs, had the musician's version of writer's block.

"Everybody was sitting there waiting for me to come up with something. I just couldn't think of anything. And if I didn't come up with anything, nobody would do anything," said Iommi in in the book Wheels of Confusion: The Story of Black Sabbath.

So after a fruitless month in LA, Sabbath returned to their English roots and rented a medieval castle, Clearwell Castle, in Gloucestershire, England, to work on writing new songs. The castle was well known to bands after Bad Company had worked within its gothic halls and dungeons. Later Led Zeppelin would rehearse some songs from the In Through the Out Door sessions there.

The Riff That Saved Black Sabbath

With a ton of pressure still weighing the band down, Iommi had an epiphany in the castle dungeon when he stumbled upon the mammoth riff that would becometitle track and savior of the band.

In an interview with Guitar World, Butler tells how low the band was before Iommi came up with that amazing riff: "We almost thought that we were finished as a band ... Once Tony came out with the initial riff for 'Sabbath Bloody Sabbath' we went 'We're baaaack!'"

Certainly the spookiness of the castle served as an inspiration for Sabbath, who soon discovered a ghost lurked within the walls.

"We rehearsed in the armoury there and one night I was walking down the corridor with Ozzy and we saw this figure in a black cloak ... We followed this figure back into the armoury and there was absolutely no one there," recalled Iommi in 1998. "Whoever it was had disappeared into thin air! The people that owned the castle knew all about this ghost and they said, 'Oh yes, that's the ghost of so and so. We were like 'What!?'"

Butler, in Wheels of Confusion: The Story of Black Sabbath, adds the medieval setting served as an inspiration: "It was really creepy but it had some atmosphere, it conjured up things, and stuff started coming out again."

With songs in hand, Sabbath would end up recording the album at London's Morgan Studios. It was released in December 1973, and on Jan. 1, 1974 in the U.S.

"The Pinnacle" for Sabbath

Indeed, Sabbath Bloody Sabbath is one of the band's best albums. In addition to the title track, "A National Acrobat", "Killing Yourself To Live" and "Spiral Architect" are among Black Sabbath's greatest tracks.

Iommi even called it "the pinnacle" for Black Sabbath.

Additionally, the album's cover is one of the most iconic in metal history. It was painted by Drew Struzan and is immediately with its depiction of an evil death on the front, and a good death on the back fold.

Speaking of that period in the band's history, Osbourne noted it was "the beginning of the end" for the band.

"Sabbath Bloody Sabbath was really the album after which I should have said goodbye because after that I really started unravelling", Osbourne told Mojo. "Then we ended up falling out of favour with each other."