If you remember the sex comedies of the 60s and early 70s, you'll remember that they all hinged on a very basic hypothesis: men are frequently flustered by sexy women with hilarious results. The comedy level increases as we get to more important and stuffy men, so a laborer who is distracted by a passing woman's boobs and drops wet concrete on a coworker's head is funny (provided he's not killed instantly), but a vicar who keeps inserting "breast" and "boobies" into his Sunday sermon because the same busty woman is in the front row is absolutely hysterical. For some reason, breasts tend to be highlighted over all other female body parts in these movies, which is fitting as they're the funniest.
The Vampire Happening operates largely along these lines with a Hollywood starlet arriving in Transylvania to claim an inherited family castle and finding out that her Baroness ancestor is in a coffin in the basement along with lots of torture devices and in pretty good condition considering she's been dead for over a hundred years. Both of them are played by the gorgeous Pia Degermark and the director Freddie Francis takes every possible opportunity to feature her body prominently in the film.
The story becomes a sort of dueling harlot farce. The actress is sexed up and has fun flashing the local priests and seducing everyone in the vicinity with a wang. Meanwhile, her lookalike vampire ancestor is seducing the same men but trying to suck their blood (there is a joke about the one differing because she sucks the men, yes). Then you have an older butler trying to stake the vampire and two slutty Catholic schoolgirls next door trying to get it on with some monks-in-training. In the meantime, priests, vicars, and various others get hilariously distracted by women's breasts. At a certain point, I was reminded of the joke Rick Sullivan used to make in the Gore Gazette about movies having more bared tits than a twenty acre dairy farm.
Freddie Fancis was better known as a cinematographer on films like Glory and Scorsese's Cape Fear, so the film looks beautiful and the castle is an awesome set. Degermark looks beautiful too, of course. The problem is the movie's never actually, you know, funny. Nor is it scary, of course. Unless you find Benny Hill sidesplitting but a bit too highbrow, you might want to skip this one.