In 1983, Michael Mann directed The Keep, a WWII horror movie about Nazis battling a ancient Romanian wizard. Despite Sir Ian McKellen, Gabriel Byrne, and a score by Tangerine Dream, this wacky cult film's never been released on DVD.
The Keep, which is based on a novel by F.Paul Wilson, stars a group of Nazis who roll into the Carpathian Mountains in World War II. They discover a strange temple in a small village. The Germans unwittingly unleash a centuries-old sorcerer, who begins blowing up Nazis à la the last scene of Raiders of the Lost Ark. The eeevil Major Kaempffer (Byrne) brings in Jewish medievalist Dr. Theodore Cuza (McKellen) to discover the monster's weakness, a plan that is flawed from the get-go. Meanwhile, an immortal (Scott Glenn) travels to the keep to defeat the wizard using your run-of-the-mill 1980s fantasy movie artifact.
The main reason The Keep hasn't seen the light of the day is that there's no demand for it. The movie bombed hard at the box office and critics found it mostly incomprehensible. This probably had to do with the fact that the film ran out of money, and Mann's three-hour-plus first cut was pared down to 93 minutes for the theatrical release.
The strangely edited final cut makes for some unintentional hilarity. For example, the lead female protagonist has sex with the hero 5 minutes after meeting him, the villain's name (Molasar) is said only once the entire film, and characters begin running in slow motion for no apparent reason. You can tell a good film's hidden somewhere in there, but it's been remixed into a gothic slurry.
So why does The Keep have a (small) cult following? Tangerine Dream (who also scored Kathryn Bigelow's Near Dark) did the soundtrack, and The Keep was a World War II creature feature. It was also a spectacular failure for Mann, who went on to direct blockbusters like Heat and Collateral. If Panzer 88 is up your alley, it's worthwhile to give The Keep a look-see. You can watch it on YouTube, and this fan site has a ton of info.