Like a seaside landlady directing me to the dodgiest room in the house, Bethany Stock pointed to the upper branches of a gigantic oak at the edge of a field in Cornwall. 'That's where you'll be sleeping,' she said. 'Can you see?'

I could. Wasn't sure I wanted to, but I certainly could. Strapped up high between gnarled branches that jutted from the main trunk at a rakish angle, a full 50 feet above the ground, my bed for the night trembled in the breeze. You know those holiday moments when you review what you've booked and think, 'I chose this?' That's the thought that passed through my mind as I prepared to experience one of the most radical, evocative and downright uncomfortable nights of my life.

For £140 to £200, the Mighty Oak Tree Climbing Company, run by Bethany and Alan Stock, provides an al fresco dinner at tree-stump level, then up you climb by rope to spend a night in a hammock - or 'treeboat' - amid the leaves and wind and loneliness. In the morning, your breakfast is cooked for you in the treetops.

Ecolodges around the world are competing to boast the greenest credentials, but surely this - a tree - is the ultimate. Here in this wood on the Boconnoc Estate near Lostwithiel, I peered up and wondered whether, from up there, that little hammock felt as high as it looked from down here on the grass and sheep poo. I would find out soon.

First Alan, who is a qualified tree surgeon, literally showed me the ropes, strapping a groin-crushing safety harness to my midriff and telling me about tree-climbing using slip-knots and stirrups. 'It's the calm and the peace up there that people want,' he explained before showing me a scar caused by a chain-saw accident seven weeks ago, which nearly took his arm off. Gulp.

The wind blew. I practised climbing, enjoying myself no end while Beth made dinner of barbecued lamb-kebabs (was it my imagination or were the sheep in the surrounding field eyeing us balefully as we tucked into their brethren?). Then as the moon rose, it was finally time to climb - quite literally - into bed.

Clambering up the rope in the dark, using two slip-knots and a sort of stirrup for one foot took me about 20 sweat-drenched minutes. My arms ached as the ground receded and a kind of numbing insularity decorated the moment. Poised between treetop and ground, I seemed to exist in a bubble of unreality pricked only occasionally by encouraging murmurs from Alan, climbing another rope nearby.

Flipping myself, at long last, into the hammock, which had been covered by a rain sheet, was an unnerving reality check. Yes, I was harnessed up and perfectly safe. But no, I didn't really feel that way. I felt vulnerable and wimpish. My headtorch illuminated shaking fingers. The hammock - the size of a small single bed - felt so tiny it seemed impossible that I should not roll over in the night and plummet to my doom.

'Keep your safety rope and harness on,' warned Alan as he whizzed back down to camp on the ground below, leaving me feeling aloof, though suddenly calm and almost childishly happy.

Now the night itself began. How can I convey the sheer bloody awkwardness of getting comfortable up there? I had my rucksack, God knows why (I should have left it on the ground), and if you can imagine having a rucksack in a single bed, along with pillows, sleeping bag and blankets, coupled with a tree-tethered rope and a harness that felt like someone was gently squeezing my testicles all night, you've about got it.

Peering down at the moonlit ground, I could see the outline of the tree patterned in shadows on the grass. When I threw out an unwanted bag it seemed to take about 72 seconds to reach the ground, landing with a sickening thunk. Why would anybody want to spend the night up a tree, I remember thinking. But here's the strange thing - I slept.

And in my dreams I experienced fleeting seconds that reminded me that I was suspended in a tree by four straps, each one inch wide. Then these moments of acute consciousness disappeared, and I felt only secure, snug and sleepy in the flapping wind, the moving branches, the isolated bed.

Finally, with dawn, the last piece of the emotional jigsaw slid into place with the rising sun and an unusually close outburst of stunning birdsong. Surprised that I'd actually managed to nod off, I raised the rain cover draped inches from my face and peered into the bright day beyond the gloom of my little tent. Around me, but fundamentally below me, a panorama of green fields, distant woods and nearby branches and leaves combined to form a morning view of a kind I had never seen before and perhaps never will again.

It was a peculiar moment of privilege and newness and that's what it had all been about really: first terror, then snug self-delusion, then dawning gratitude.

Alan nipped up and cooked me porridge with a camping-gas stove strapped cleverly to a nearby branch. Actually, a funny thing happened while I ate. Despite the fact that I'd been up in my hammock for eight hours, I suddenly felt sharply aware of the thinness of the fabric holding me up there and wanted to get down.

Taking the rope to safety at last I felt glad to touch the ground. There aren't many times in life when you're happy just to feel your feet settle into grass and sheep poo.

Essentials

Tree camping, including breakfast and dinner, costs from £140pp in a group, £200 solo with the Mighty Oak Tree Climbing Company (01637 880466; www.mighty-oak.co.uk). It also provides recreational tree climbing sessions from £30pp. Nicholas Roe flew from Gatwick to Newquay with Air South West (0870 2418202; www.airsouthwest.com) which has four flights daily, from £58 return.