I bumped into this movie in Cinemax during the mid to late 2000s, but the movie looked older than that. From what I remember, it's a horror movie (I'm thinking the slasher kind, but I'm not sure) that takes place in a large castle or castle-like mansion during a party with a bunch of people aged from late teens to mid-20s wearing attires that look like they belong in a prom or dance. The party had loud music and club-like dancing so the attire may have been formal (probably because of the very high class rich person venue), but the party kind of wasn't. I remember it was VERY bloody and violent and it probably had some form of nudity or partial nudity (probably censored for tv).
The characters are killed off one by one. I only remember 2 of the deaths:
1. While the party is going on, in a hidden room, one of the girls are bound in an upright position with her arms strapped to posts spread above her head. She's screaming, but the music is too loud for anyone to hear. As she is bound and screaming, long needle-thin spikes come out from the torture machine slowly impaling through her body one at a time in different parts of her body. By the time the main characters find her, the floor is covered in blood and the girl is like a pincushion impaled with multiple needles and she says the line "Help me." before finally dying.
2. While the characters were searching for something or someone they enter a bedroom with a four-poster bed that has drapes covering the top part (hiding a dead body). As a female main character enters the room, it's a jump scare as the bloody body falls from the "ceiling" of the bed with its legs still tied to the top so it's upside down when it finally comes to rest. Her friends rush in when they hear her scream and the body is revealed to be one of the male main characters.
I forgot what happened in the ending, but as far as I remember, everybody is dead except the MAIN female character who survives and she walks out the front door.
Movie ends with an outdoor scene where we see the female lead walking out of the castle/mansion. The mansion is on the left of the shot and in the background is a beautiful landscape (mountainous, I think). As she walks from the mansion on the left all the way to the right side of the shot, credits appear and roll on the background-filled space of the shot.