The term Seven Walls (七つの壁, Nanatsunokabe?) indicates an inter-dimensional place, accessible only through a particular "entrance", which represents an imaginary barrier that separates  from the rest of living beings. The Seven Walls are actually an allegory to indicate space and time, and therefore the only way to go beyond the Seven Walls is to transcend the laws of space-time, using one's own subconsciousness and imagination within this place.