In Franz Kafka's The Trial, the main protagonist, Joseph K., finds himself arrested without knowing (or indeed without ever finding out) the reasons why, wandering through corridors and frequently entering and leaving a number of rooms through doors. Therefore, doors, and one could argue even windows, play a big symbolic role in this novel.
Windows and doors form openings in rooms. Through this newly created space in a door, two formerly divided rooms suddenly become connected. Therefore, windows and doors in The Trial can be seen as metaphors for the fact, that it is always possible to open up borders by creating a connection. These borders can be physical (such as a wall between to rooms), but also psychological (such as people, who disagree). However, the doors don’t always open—“looking at the door which did not open again”—indicating that these connections are not always working the way they should, representing the difficulties in life people can face.
Doors enable people to look inside as well as to look outside a room. The first door through which Joseph K. enters in the novel could be seen as the beginning of Joseph K.’s journey through a labyrinth of doors, struggling to find his way. Some doors Joseph K. faces are “already wide open” while other doors are opened for him: “she opened the door to Miss Bürstner's room.” There are others that Joseph K. is unable to use; for example, “she [Miss Bürstner] locked the door,” thus making it impossible to enter or re-enter a room through this very door. This can be interpreted as a metaphor for the struggle of trying to find one's way in life: doors open, close, or sometimes refuse to open. These doors are symbols for the various possibilities and options one faces in life.
Similarly, windows allow people to look inside or to look outside, giving people a different perspective: “who had come close to the window opposite so that she could continue to see everything.” Like doors, they can be opened, closed and locked.
Therefore, in this novel, doors and windows are used as symbols for life; one spends most of their time searching for the meaning of life by wondering through a metaphorical labyrinth of doors within the metaphorical building that is life, eternally searching for the purpose by opening and closing these metaphorical doors.
At the same time, Kafka underlines through this metaphor the futility of this quest, as Joseph K. never finds what he is looking for, regardless of how many doors he opens and closes—just like humans keep on searching for the purpose of life without ever finding it.