They must have been vampires
At 1st I thought the spooky inhabitants of the castle were mere ghosts.
But later on it turns out that these so-called ghosts needed the blood of the
living to survive.
Now unless they are vampires how is that ghosts would need the blood of their
victims to live?
That one scene where that shirless man kills Carmus/drinks his blood by biting
him in the neck is the behavior of a vampire rather than a typical ghost.
Maybe this world is another planet's Hell. - Aldous Huxley (1894-1963)