Garderobe entered the English language in the 15th century and continues in use to this day, though its frequency has diminished significantly since the 19th century. Originally, its primary duty was to provide English speakers with a word for a room or closet in which to store clothing. Later, by extension, it was used for private bedrooms and bathrooms. Today you are most likely to encounter the word in a description of an old castle, such as our example sentence. "Garder," the French word for "guard" on which "garderobe" is based, has also served English well by directly contributing to the formation of such words as "award," "guard," "regard," and, yes, "wardrobe."