The beauty of
Picnic at Hanging Rock is how much is left unexplained which only serves to emphasise the mystery and sense of terror about what happened to those girls. Whether or not it's based on true events, it's one of those strange films which can easily be classed as a horror film without any true horror, simply due to the atmosphere and sense of unease with which it leaves you.
The recent Blu-ray release is superb and, if you don't already own it, you should really added to your collection.
Picnic at Hanging Rock: Director's Cut Blu-ray Review