(Slight word of warning, if necessary: this is just over 2 hours long, and being with subtitles and full of dialogue, much attention is needed thoughout)
Sensually the film has much to enjoy - the mediterranean sunshine, beaches, plenty of (often naked) eye candy for both sexes, and a decent soundtrack with notably a piano playing at 'significant' points in the flim
As others have commented the film revolves mainly around half-a-dozen late twenty-somethings and their intertwinings, emotional and physical, with a couple of very explicit sex-scenes both with brief (blink and you'll miss them) pornographic moments. But I'm going to sound a bit pretentious and suggest that the other viewers have mostly missed the main theme of the film
Although Lucia (and the sex) major in the film the main character for me is Lucia's boyfriend, Lorenzo. And what does Lorenzo do? He's a writer! And what do (fiction) writers do? They make things up! And that to me is what this film is really about - the art/process of writing, using imagination, making things up, and living/not living in what others see as the real world
Arguably the writer and director of the film are indulging themselves regarding the creative/writing process: its benefits (for the writer) and the effects it has on their lives and other people they know, and the rest is essentially subtext. Both Lorenzo and Elena separately say something like: " .... the beauty is you can stop half-way through and start again". Stop and restart what? What is the signifcance of the hole in the beach? Is anything/anyone ever actually seen there? Where does a writer, or anyone when 'creating', go? At one point Lorenzo, seeing the effect his story/writing has on Lucia, dashes off saying: "I must kill them off!" With a gun? 'Course not, but with his keyboard
Near the end of the film Elena is seen looking at Lucia, Lorenzo, and his friend Pepe. Seconds later, at the exact same place, the three have vanished, and instead we see her looking through a doorway at a computer tucked away in the corner of an adjacent room. So where have they gone, and how? Hardly difficult to work out, surely
Utimately this is another film where arty types are talking about themselves and what they do. It's okay I guess, (especially if the creative/arts world is your scene), and i'd recommend it for watching at least once, with its mix of scenery, sex, inter-personal drama, etc, but essentially it's ALL a story - a story within a story