A subterranean lavatory is not, in itself, a mysterious place. If cleanliness is next to godliness, it may seem perverse to go underground in search of it; but that is a minor paradox.  Busy streets simply demand a small collection of toilets and handbasins at this corner or that—so it was in Toronto in the early years of this century, and so it remains in such cities as London and Paris, which continue to acknowledge the merits of the gentle, periodic descent.  It is not a mystery that they appeared.  It is rather a mystery that they disappeared.  Toronto’s first one seems to have been built just as Queen Victoria was exhaling for the last time.  No one is quite sure—records were not kept until five years later.  Like many more or less obscure painters from the hazier centuries, the birth of the downstairs lav in Toronto must be noted as "circa 1901."  But while the demise of such painters was quite often recorded, that of the underground lavatory remains troublesome. (from John Ferguson, "The Ivory Cellar")
The break should occur where the author moves from a general discussion of underground washrooms to a specific discussion of those located in Toronto.