Nightmare Castle is a good old fashioned horror film that pulls no surprises but still tells a good story. This is the kind of stuff that belongs on late night fright television. Barbara Steele is great in her dual role as two identical half-sisters. [Just go with it!] Her performance is very theatrical and dramatic in a good way. The rest of cast is solid as well.
The story begins with Lady Arrowsmith [Barbara Steele] who has a torrid love affair. She is caught by her jealous husband, Dr. Arrowsmith, who tortures and murders both her and her lover. The good doctor then takes Lady Arrowsmith's half-sister as his wife who continues to be haunted by her dead half-sister. I'll let you figure out the rest for yourself.
Nightmare Castle is available as a free download. It is an Italian film that is dubbed in English but don't let that scare you away from the film. All in all, a solid effort.
Download a copy of the film from Archive.org
For more info check out the film's entry in IMDB.