Alain Robbe-Grillet is an accomplished writer of novels (like "Jealousy") and screenplays (like "Last Year in Marienbad"), but in the 1970's he turned to the sex genre not because he was really that interested in making sex movies, but because it gave him a forum he wouldn't have otherwise had to continue making his experimental, surrealist art films (and to have them seen by anybody). In this respect he was kind of like his fellow countrymen Jean Rollin and Walerian Borozyx and (some would say anyway) the Spaniard Jess Franco.
It's hard to describe this movie. It involves a kidnapping, a brothel, a strange criminal gang in bowler hats, and a bourgeoisie couple and their maid, but even the characters are fluid and seem to transform into each other, and cinematic time and space are so re-arranged that it seems to take on the illogic of a dream. If you enjoyed "Last Year at Marienbad", you'll probably enjoy this, but if you're not such a fan of that movie there's also the added attraction of a bevy of Euro-beauties like Anicee Alvina, Agostina Belli, Joelle Coeur, and Sylvia Kristel all getting (more-or-less) naked. So this a good movie for the arty and/or the horny.
Unfortunately, it is not currently available in English (though I doubt it would make any more sense), but they recently released one of Robbe-Grillet's other later films, "La Belle Captive" on a subtitled DVD, so hopefully it won't be too long until they get around to this one.