Curse of the Crimson Altar (1968)

"Come face to face with naked fear on the altar of evil!"

When his brother disappears, a man visits the remote country house where he was last seen. While the host seems outwardly friendly and his niece more demonstrably so, there's a feeling of menace in the air with the overhanging legend of Lavinia Morley, the Black Witch of Greymarsh.