When you watch enough of these, you start seeing cool titles like Bloody Pit of Horror and thinking, "Uh-oh, I hope they didn't think of the title and make the poster before they actually wrote the movie." I suspect that's the case with this thing, as plot is not at all a huge consideration. Nothing says I'M CHEAP AS HELL like a prologue in which the only sound is a narrative voiceover. Medieval serial killer The Crimson Executioner kills people who don't live up to his moral standards. Society thinks this is wrong, so they kill him. In an iron maiden that looks like a ride car from a really third-rate carnival.
The Marquis de Sade gets top billing and a swanky pencil-written animation, a big clue that the exploitable element in this exploitation movie is gonna be torture. And, indeed, a bunch of models and a few of their dudes travel to the ancient castle of the Crimson Executioner. Because that is where you do your photoshoots.
They're summarily tortured and killed. We the viewers might not be killed, but you can't say we aren't tortured. Because this is a 1965 film, which means the girls wear Gidget/grandma underthings and the blood is sparingly shown. As a boring workaround, we get elaborate, Bond villain-style traps, including the shitty giant spider below. I would estimate that the hero takes 15 hours to scuttle underneath all this webbing and reach this girl. And this is one of the film's high points.
Typically, the movie's whole reason for existence—torture—gets saved for the very end. These are tortures that you can enjoy with the whole family, like tying a girl to a rock thing or making girls spin on a wheel in their underwear. One would guess that the film derives from those Betty Page bondage shoots or maybe the fifties sexploitation roughies, but I feel bad for the pervs of the sixties if this is how they had to get their kicks.
This (obviously) lacks the class of the best horror of its era, but also can't match stuff like the H.G. Lewis films for sheer brutality. So Bloody Pit sits in a boring, midway limbo, which is where you will leave it, if you are wise.