A very interesting question as she does not physically even leave the house. Symbolically, however, Mrs Mallard travels outside the boundaries of her marriage in to the wide open spaces of freedom and independence. She contemplates the shortlived sadness she will feel at the funeral of her husband, but then revels in the idea of years of solitude;
...a long procession of years to come that would belong to her absolutely. And she opened and spread her arms out to them in welcome.
Mrs Mallard - by now Louise - can see the vastness of the world before her, all as she is locked in her bedroom digesting the news of her husband's death -
Her fancy was running riot along those days ahead of her. Spring days, and summer days, and all sorts of days that would be her own. She breathed a quick prayer that life might be long.
Sadly, everything for Louise is taken from her as she dies of shock when discovering her husband is alive. Maybe her journey is over, or perhaps she has to travel a little futher beyond this world to achieve the perfect peace she desires.
In "The Story of an Hour", Louise runs away to her room after hearing from Richards that her (Louise's) husband had been killed in a train wreck. Being that she has poor health, defined in the story as "heart trouble", the news is given to her as succinctly and yet as tenderly as possible.
At the most literal level, the symbolic journey that she takes occurs in her mind, but it is also aided by the window in her room. This window appears to have served as a type of oracle for Louise--one through which she would visualize her freedom, and herself, as something other than a married woman and housewife.
There stood, facing the open window, a comfortable, roomy armchair. Into this she sank, pressed down by a physical exhaustion that haunted her body and seemed to reach into her soul.
The story further explains that the square that makes up the frame of the window served as an agent of visualization, which (like a painting, a screen, or even a modern TV), would allow her to see tree tops, nature, and all the wide open spaces from afar. These are the very spaces that she wishes to occupy. Mrs. Mallard is more wild in spirit, much stronger, and much more passionate about things than what her current status as a society lady lets her show. It is no wonder that she felt relieved and liberated upon finding out about the death of her husband.
There were patches of blue sky showing here and there through the clouds that had met and piled one above the other in the west facing her window.
As the window is mentioned nearly 3 times in a row, we cannot deny its importance as the niche that Louise may have preferred throughout her marriage to see the world outside of her home. As a woman of her generation, she must have been asked to embody the crux imposed upon all women of her time, to be the "angels" of the household. Hence, Louise Mallard lost herself in the process of becoming "one with her husband". She obviously resents that, and the liberation from her husband represents a chance to lead another type of life.
It also comes to no surprise that, upon her mental return from the fields and "blue patches of sky" that constituted her future and potential freedom, she literally drops dead at the sight of her (very much alive) husband entering the home. It had been a misunderstanding; Brently was not dead. So Louise had a heart attack which was ironically confused with "joy that kills".