Have you spoken to the innkeeper about the cellar and what's down there? You'll need to have read her husband's journal, I think, before she'll discuss it. (Going from memory here!)
After that, the candle is accessible before you even descend the steps to the cellar. The little window is close to the ground from the upper level, so perhaps at first easily missed.
"Bleat, Watson -- unmitigated bleat!" ~ Sherlock Holmes