I saw this movie when I was very young. It would have been early 80s and was on television but was probably from the 70s.
From what I can remember, the film starts quite normally and is located in the countryside. A some stage, a man goes into a river mill cabin. In here it starts to turn weird and he either melts or burns. (I can’t clearly remember as I was very young, however it disturbed me for a long time).
Don’t think it big movie but hope someone can help on the above.