Devil's Nightmare is a Belgian/Italian horror movie released in 1971. Directed by Jean Brismée, it tells the story of seven tourists who become lost during a trip in Europe. A strange man by the roadside shows them the way, but as it's too late to catch the ferry, they are then directed to a castle where they can spend the night. There, they meet a succubus (Erika Blanc) who kills them because they represent the seven sins.
In Belgium, where the film was shot and released under the French title
La plus longue nuit du diable, hardly anyone knows of its existence. However, it was quite successful in Italy. Since then, it has been released under an array of different titles, so you may also know it as
The Devil Walks at Midnight,
Nightmare of Terror, Vampire Playgirls,
Castle of Death,
La terrificante notte del demonio,
Au service du diable, etc.
This strange mix between
The Pit and the Pendulum and the Euro trash films of Jess Franco and Jean Rollin, was almost entirely shot in and around a castle in Belgium:
Château d'Antoing or Castle of the Princes of De Ligne, which was first mentioned in the 12th century but rebuilt by architect Clement Parent in neo-Gothic style in the 19th century. It's one of the country's most beautiful castles, so whether you've seen the film or not, it's worth a visit when you're in South West Belgium or one of the neighboring cities in France.