Godland is a film to see on the big screen: not just for its awesome, immersive cinematography, but because it is so remorselessly bleak that if you’re watching it at home you are likely to give up. To get the most out of it you need to be trapped.

Lucas (Elliott Crosset Hove), an upright, serious, bearded young Lutheran priest in late 19th-century Denmark, is being sent to Iceland as a missionary. ‘Lucas, you must adapt,’ his red-faced bishop (Waage Sando) tells him while munching through a lavish lunch of chicken and boiled eggs. ‘At times your task will seem monumental.’ The Icelandic weather is forbidding, the bishop explains; in the perpetual summer sunlight people forget to sleep. A volcano has recently gone off whose ‘smell can be so overwhelming that people lose their minds’. The young priest sits there, not eating a morsel. The viewer reflects that the running time is 143 minutes.

On disembarking, Lucas meets his guide through the wilderness: Ragnar (Ingvar Sigurdsson), a weatherbeaten atheist curmudgeon who refuses to speak Danish. He slightly reminded me of the only Icelandic tour guide I have encountered, who shepherded our group towards a ravine and then announced: ‘If you go on the other side of the rope, you will die.’ By the time we had discovered how flimsy the rope was and how slippery the path was, he had disappeared round the corner for a fag break.

So I could feel some extra sympathy with Lucas, Ragnar and their little party as they trudge over miles of jagged mountain and spongy, rain-saturated moss, occasionally pausing to gather round the fire and listen to an unsurpassably creepy story about a traveller whose life is ruined after he stumbles on an evil population of eels. The camera lingers over the entrails of a butchered sheep, or a worm crawling on a pile of horse dung in a downpour. ‘You look miserable,’ a farmer tells Lucas, not inaccurately. ‘Ragnar,’ Lucas eventually gasps, speaking for us all, ‘I can’t do this any more.’

Yet by now, the landscape has begun to reveal a sinister beauty. The volcano, when it appears, slithers and spits and oozes so majestically that I realised my mouth was literally hanging open. In one tracking shot, the travellers’ path through the mountain slowly disappears into the mountainside itself, the craggy, impassive face of a giant. The director Hlynur Palmason has a remarkable gift for the visually sublime – sublime in the old sense of ‘terrifying’.

Meanwhile, the film is dropping hints. That slaughtered sheep: shouldn’t it remind us of the Lamb of God, killed for our sins? The basket of gleaming fish that Ragnar pointedly presents to Lucas one morning – how can we not think of Jesus’s image of the missionary’s work? When the travellers cross a perilous river, isn’t it the Exodus all over again?

Yet having built up this atmosphere of foreboding, the film squanders it. Theologically, it goes nowhere. The intriguing Ragnar gets less intriguing the more we get to know him. Lines that are supposed to sound pregnant with meaning just come across as flat. Characters start randomly converting to Christianity, or falling in love, or committing terrible crimes, for no apparent reason except to drive the film towards the tragic denouement it desperately wants to have.

After the tragic denouement, the camera settles one last time on the unforgiving landscape while the Copenhagen University Choir sing a rousing tune about ‘Denmark, my fatherland’, as if to ram home the bishop’s observation that people in Iceland get no sleep and lose their minds; which perhaps they do. But not, surely, like this.