Atrocious: Adjective: extremely wicked, brutal, or cruel;: appalling , horrifying.

From “The Yellow Wallpaper”, ” I am sitting by the window now, up in this atrocious nursery, and there is nothing to hinder my writing as much as i please, save lack of strength.”(Page 2, paragraph 8)

Now i understand that the narrator believed that the nursery was a scary place  to be in.