Why is the setting of "The Oval Portrait" important? How does the chateau contribute to the interpretation of the story?

In describing the Chateau that the narrator and his valet come to find while seeking refuge in the night, Poe paints a picture of a place that was once very grand, and is now falling to pieces. While beautiful, the setting is very ominous, as the narrator states that it was "one of those piles of commingled gloom and grandeur which have so long frowned among the Appennines." Who lived in this chateau? Why has it now been abandoned? It all adds to the mystery. Poe is setting up an environment that creates suspense, just as he does in a lot of his work.
This narrator breaks into a dilapidated manor in the middle of the night, somehow in a "desperately wounded condition." He and Pedro, the valet, choose a small room, close all the shutters, and light candles. The narrator admits to being delirious, and begins to obsess over the portraits in the room. With tension built up so well by Poe's dark and eerie setting, when we finally get to the oval portrait, lurking in a dark corner, we know as well as the narrator does that this is no ordinary painting.