This is an above average example of the type of metaphysical horror film that seemed to proliferate in Europe in the 1970's.
It's simply the story of the Devil, his minion (the succubus) and seven tourists (each representing one of the seven deadly sins) who are forced to spend the night in a sinister castle.
The first hour is rather plodding due to an over abundance of exposition and very little action. Viewer patience is rewarded however during the final half hour when Ilse (the succubus) starts doing what she does best.
Erica Blanc is superb in this role and her transformation from sexy seductress to ghastly succubus is a highlight. Another highlight is Daniel Emilfork as the Devil. His performance is a real stand out when compared to the rather wooden performances delivered by some of the other cast members.
Director Jean Brismee also deserves kudos for several delightfully imaginative flourishes during the death scenes.
All in all it's worth watching if you're a fan of this type of film, but it's definitely not one of my favourite Euro horror films from this era.
6 out of 10.