Viy is a 1967 Russian-language horror film based on a Gogol short story. Though Gogol claimed a folkloric source, no such source has been found. The story concerns a seminary student engaged in a 3-day vigil over the body of a witch. Some of the special effects are interesting, but I probably won't watch this one again. There's just not all that much to it.
Watching movies via youtube is iffy and isn't a substitute for seeing them on DVD. I spend time waiting while the video buffers, or I have to re-start a video which doesn't recover from an episode of freezing up. It's great for pre-viewing films, though. I've found some real gems this way.
The MosFilm channel at Youtube has the movie online, but embedding is disabled. I can't find a trailer, but the first 15 minutes is embedded below:
This film has a spot in the book 1001 Movies You Must See Before You Die. That author calls it "a coloful, entertaining, and genuinely frightening film of demons and witchcraft that boasts some remarkable special effects work".