Turkish auteur Nuri Bilge Ceylan’s last film, Once Upon a Time in Anatolia, was the joint winner of the Grand Prix at Cannes in 2011, and it became one of the most highly praised movies of recent years. Its follow-up, Winter Sleep, has now won this year's Palme d'Or. But considering the number of people who were having naps during the screening, it also would be hard to call it an unalloyed triumph. Far less eventful than Once Upon a Time in Anatolia – which itself had a certain woozily soporific quality – it’s essentially 196 minutes of long, involved conversations about ethics. Viewers should have strong constitutions, and lots of strong coffee, if they’re planning to watch it.

One thing that everyone should agree on, though, is that its rural Turkish setting is extraordinary. The characters live in a spectacular mountain region where the rocks resemble huge blobs of meringue and where some of the houses are built into these rocks. When the inevitable Lord of the Rings remakes get underway, the filmmakers could do worse than to shoot their Shire scenes in the area.

It’s in this remote, fairy-tale landscape that the film’s hero, Aydin (Haluk Bilginer) owns a chalet-style hotel. It doesn’t have many customers, especially not during the snowy winters, but Aydin isn’t too bothered. The richest man in the community, he is a greying former actor who doesn’t want any guests who don’t “appreciate the natural setting”. If there are none around, he is content to while away his time in his snug, book-stacked study, typing a weekly opinion column for a tiny local newspaper, and researching his definitive History of Turkish Theatre.

His other responsibility is a house he owns in a nearby town. The tenants haven’t paid their rent in months, and while Aydin feels he is being generous in letting them stay, some of the family members resent him: early on, there’s a jump-out-of-your-seat moment when a young boy throws a stone at Aydin’s Land Rover, turning the passenger window into a spider web of cracks.

The attack seems to presage more violent confrontations, but after that moment the cracks in Aydin’s life are all metaphorical, and they’re caused by words, not sticks and stones. His stunning, much younger wife, Nihal (Melisa Sözen), who’s sure to be snapped up by Hollywood), has set up a charity, but she feels neglected when Aydin doesn’t participate, and she feels stifled and belittled when he does. Meanwhile, his divorced sister, Necla (Demet Akbag), despises his complacency and loathes Nihal. Like one of Chekhov’s Three Sisters – a clear influence on the film – she also wishes she was flourishing in Istanbul, instead of languishing in Anatolia.

With no guests to distract this trio of increasingly disgruntled housemates, it’s time for some shouting matches, some crockery smashing and even a gunshot or two. Well, it would be in the average film. In Winter Sleep, however, it’s time for some incredibly lengthy and measured philosophical debates in which people say things such as, “The disguise of lyricism makes you stink of sentimentality.” I don’t think I’ve ever witnessed such protracted dialogue scenes in a film before. And if that weren’t enough to explain why some viewers were in need of a snooze, the actors all speak in soft, velvety voices, while wrapped in knitwear and nestled in comfy chairs in shadowy, cave-like rooms. The camera doesn’t move, and there’s no incidental music, just the crackle of log fires or the patter of rain to accompany the theorising.

Still, if you can stay awake, you’ll be struck by the nuanced performances, the breadth and depth of the characterisation, the intensity of the moral questions, and the drips of black humour. More importantly, Ceylan conjures up a mesmeric, dreamlike atmosphere which suggests that his characters are somehow cut off from the rest of reality. Winter Sleep is a remarkable achievement from a unique writer-director. But whenever one of its calm, meticulous arguments reaches the 15-minute mark without showing any signs of being resolved, you may start hoping for someone to fling a stone at a window and have done with it.

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