This was possibly the most atmospheric RPG session I had (years and years ago), where I GM’d Gary Gygax’s Dangerous Journeys RPG. I had my party head-hunted by the priest of a large town to deliver a small package to a friend of his in an outlying border, where his friend ran an Inn.
They arrived at nightfall, and the Inn was silent and dark. I ran it like a macabre horror.
The package was a holy symbol, the innkeeper had requested it because he thought his Inn had become possessed… in reality a demon lived in the bottom of the well, and came out at night… it was classic.