Borges, "The Library of Babel"

The first paragraph, on close reading, gives a surprisingly nonsensical physical description. Only one of the open sides of the hexagon is described as opening out into another. Does the other side really do likewise, as one would naturally assume? If so, are these sides opposite each other, resulting in a single infinite row of hexagons? (There can be no hexagons to either side.) Then again, how does a single mirror in the vestibule (not in the restroom-compartment?) produce the illusion of infinity? And, for that matter, why would so many restrooms be necessary? (Perhaps the Freudian link between books and anal erotism...)