Many libraries, many places, time immemorial-ongoing.
Students at many colleges and universities claim that sex in the stacks is common, sometimes even a rite of passage before graduation. It is unknown how much actual sex in libraries takes place, but a review of the literature and an informal poll suggest that sex in the stacks is more of a myth than a reality. http://www.thecrimson.com/article.aspx?ref=505583, http://library.duke.edu/blogs/answerperson/perkins-lobby-edition/