The room in which the narrator of this excellent short story is, to all intents and purposes, trapped, is actually the former nursery of the secluded house where she is forced to repose by her loving husband. If we have a look at the first section of this story, the narrator herself describes this room to us:
It is a big, airy room, the whole floor nearly, with windows that look all ways, and air and sunshine galore. It was the nursery first and then playroom and gymnasium, I should judge; for the windows are barred for little children, and there are rings and things in the walls.
However, apart from this general description of the room, what is centrally important about it, and what gives the story its title, is the yellow wallpaper that twists and turns so fantastically with a pattern that is described as "One of those sprawling flamboyant patterns committing every artistic sin." It is this wallpaper that comes to symbolise the repression and imprisonment of the narrator, and finally indicates her descent into madness, as she comes to inhabit it.
I think it's important to note that the narrator's first impressions of the house where the room is contained is "a colonial mansion, a hereditary estate, I would say a haunted house." There is an element of mystery as well as seclusion. The speaker says, "I don't like our room a bit," and says the windows are "barred." She mentions that the "paint and paper look as if a boys' school had used it" and that "it is stripped off" and in "great patches all around the head of my bed." The narrarator spends a great deal of time analyzing the colors of the wall paper and decides that it is changing.
She describes the furniture as "no worse than inharmonious" and spends a lot of time in the "great immovable bed" that is "nailed down."
Hope this helps.