In Matrix Revolutions we are introduced to the Key Master. The Key Master has access to all the back doors in the Matrix. To spell out what that means, in the virtual world of the matrix the Key Master can open doors which instead of leading to what is usually on the other side, can lead to another back door. All of these back doors can be accessed from a hallway filled with these doors.
This set up turns the entire world of the Matrix into a maze of doors leading to doors. The center of this maze is the door leading to the Architect who, as you may suspect from his name, built the Matrix.