The film is actually a deeply moving fantasy storey of a young girl (Ophelia) who is court up in the Spanish civil war. When she goes to live with her mothers new husband (a captain in the army) she finds a labyrinth nearby. In the labyrinth she finds a faun who tells her she is really a princess of another world and sets 3 tasks for her to accomplish in order to open a gateway back there.
As the film is actually Spanish the English title is actually a mistranslation, with the original title actually meaning something along the lines of The Faun's Labyrinth and the film has very little to do with Pan. Not sure why they renamed it though?
The film easily justifies it's 15 classification with some graphic violence and the deeply emotive portrail of the captain's treatment of Ophelia, her mother and a number of other the characters. It can be quite disturbing in places.
I was particularly impressed with the ending and the way the film left you not quite sure whether the fantasy parts had actually been real. Whether she'd gone back to the other world or whether this had just been her imagination sparked by her unhappiness and inspired by the numerous books she had read. The later being more disturbing as it meant the main character who you had become quite attached to by the end of the film was actually really dead.