Probably 70s weird movie

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.

Thanks.

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