In the year 1900 in Australia, a group of girls from Appleyard College, which seems to be little more than a bourgeoisie finishing school, go on a picnic to Hanging Rock, a beautiful, and craggy geological formation on the edge of the bush. Several students and one of their teachers vanish without a trace. This story is rumored to be based on truth, but as far as I can tell, it is entirely fictional.
In the novel upon which Picnic at Hanging Rock is based, the author actually included an explanation of what happened to the girls who disappeared. When it was published, this piece was left out because the story is so much stronger without it. One of the prettiest of the differences between fiction and real life is that in the fictional realm, no explanation is necessary. Real life doesn't offer that kind of poetic power. If the girls had disappeared in real life, there would be an answer somewhere, and during sweeps season, the hard-working scientists on CSI would find it. In Peter Weir's adaptation of Picnic, there is no causal explanation, no physical evidence, only speculation that the girls did not belong in the world they found themselves in, and thus, ceased to exist.