I stumbled across The Terror one night many years ago, and I STILL have no words to describe this film. Although I've seen it several times since, have read the movie cover description over and over again - the actual film still doesn't make much sense.
That said, it's so absurd, so strange, and such a classic that you must watch it. Must. Here is the movie description, per the case. Note: read it as much as you want, it will be of no use to you when you watch the movie.
"In an early career appearance, Jack Nicholson stars as Lieutenant Duvalier, a nineteenth century military officer whose dreams are haunted by a mysterious beauty (Sandra Knight). Those same dreams draw him to the sinister castle of Baron Von Leppe (Boris Karloff), but is it really the Baron or an impostor Before he knows it, he finds himself a prisoner and frantically tries to solve the mysteries that surround him. Director Roger Corman collaborated with other directors, including Francis Ford Coppola, in the filming of this horror classic."
If you want to embark on this adventure you can watch it now for free through the Internet Archive!