On a rutted farm track on the edge of Bodmin Moor stood a ramshackle, scuffed white farmhouse, its windows and doors a faded, though jolly, blue. Inside a disparate rabble of girls shouted and giggled, intoxicated on fresh air, Beatles albums and the freedom of being far from their parents on their week-long pony trekking holiday.

I was among them. Not shouting but giggling, perhaps, as some of them toasted sliced white bread, burned on one side, which they ate with margarine from an industrial sized tub and synthetic red jam which had never been anywhere near a strawberry.

The old farmhouse had been gutted and refashioned into a teenagers' paradise: Two dorms, each containing eight bunk beds, a shower with a mouldy vinyl curtain and a separate toilet, always smelly, a metal hook in place of a lock. Downstairs was a large living area with a fireplace, a long, wooden, refectory-style table and a sideboard with a record player, a selction of scratched LP records and a toaster. I don't recall a kettle, or if any of us needed one. I was thirteen, and I still rode hobby-horses when I wasn't lucky enough to be near a real one.

No matter our background, these holidays were the highlight of our year. We arrived alone, bonded quickly, exchanged addresses on leaving, and never wrote. This was the early 1970's: if you had a friend who lived far from you, you wrote letters on pale blue Basildon Bond writing paper until you ran out of things to say, or you grew up and forgot who you'd been, and who had meant the most to you. While we were there, however, the farmhouse hospitality, the ponies and the windswept tors up which we galloped through waist-high bracken and babbling streams, were our entire universe.

All of us had a crush on Nick, who ran the holidays. Young, fit and charismatic, he seemed to us to be made from the very bedrock on which we stood. He was wild and woolly in a dishevelled Poldark way, with oceans of untamed black curls, a folk singer's beard and laughing blue eyes. He walked around the yard with bare chest and wellies. The ponies loved him. We loved him, especially when he told us stories.

Each week, trekkers would be treated to an overnight expedition. Riding much further than usual, past the awe-inspiring Cheesewring and sleeping side by side on straw in an old barn, this year was following the usual pattern. We all snuggled up in our sleeping bags, Nick somewhere in the centre, in charge of the single candle and the flickering shadows on the wooden ceiling. Nick began telling us stories. We never tired of his tales: wild ponies, magnificent birds, a childhood on the farm, colourful local characters and ancient Cornish traditions were spun golden until our eyelids grew heavy. Being teenagers, we also loved a ghost story and, said Nick, Cornwall is full of ghosts.

On this night he told us the story of Tin Pan Alley, now a gently flowing stream at the end of the track, which we crossed with the ponies each time we rode onto the moor.

The story has it that in centuries gone by, a tin mine here had collapsed, killing and trapping several workers, some of whom were said to roam the 'alley' still. Nick said he had never seen a ghost, but he knew a few people who refused to cross the stream at night. We were silent, rapt, as he blew out the candle and bid us goodnight.

The following day as we rode back to the farm, the grey clouds seeming to add extra menace to the previously benign moorland, we were still thinking about the story of Tin Pan Alley. As we crossed the stream we asked Nick if he'd be willing to take us back there, after dark.

A few of us were too scared to go, at first. The majority though, were treating it as a harmless adventure, an extension of the story, as if the location itself would make it come alive in our imaginations, if not literally.

Some of the girls made toast. We were all chattering excitedly. At around 10 o'clock Nick came to collect us and he brought along Rosie, the soft-natured dog from the next farm who thrived on teenage cuddles and sometimes trotted beside the ponies on our shorter treks. For safety, he declared, with a twinkle in his eye. We understood that Nick did not believe in his story. Not truly. He was winding us up into girlish hysteria as part of the game, but he never fully intended us to believe it was anything more than an evening excursion.

The evening was damp and still. The moon, mostly obscured by clouds, peeped out now and then illuminating the fields and hedgerows in a milky glow, before slipping back behind its cloak of darkness, leaving us disorientated. Very slowly and gingerly, all in a row, we picked our way. The path was narrow and stony; to one side a wall covered in brambles, the other side, grass sloping down towards the stream as it gurgled away from Tin Pan Alley. It felt as if we were walking for miles; Nick at the front, talking in whispers. I was at the back with Rosie, and a plump girl called Louise who was sniffling and holding onto the back of my jacket. We jumped at every shadow, yet we felt excited as we inched forward.

Suddenly, Rosie sat down in the middle of the track, whining and refusing to move. 'Wait!' I shouted to the others, as I tried to coax the dog forward. I didn't want to be left behind! Louise's sniffles turned to sobs as Rosie stood up, wheeled around and fled back up the path towards the farmhouse, Louise hot on her heels. A few of the girls shuffled restlessly and I could sense that even Nick found this development strange, Rosie being the most placid dog imaginable. Everyone seemed rooted to the spot for a few seconds as some considered whether to abandon the mission. Just then the clouds sprang apart and moonlight flooded the grass beside us. A communal gasp rose up as there, silhouetted just meters from the path, appeared a dark, shadowy shape. As my eyes tried to focus, the form appeared to me as that of a man with a yoke across his shoulders, a pail at either end, something on his head. I stared, blinking, not quite trusting what I was seeing. Were my eyes swimming from the dark, was I allowing the collective hysteria to stoke my imagination beyond what I was actually witnessing? It was impossible to tell. I was taking no chances. As girls of every shape and size pushed past me I joined the stampede, the adrenaline carrying us laughing, crying and screaming like the banshees we sought to escape as we tumbled back into the farmhouse where Louise sat white-faced at the table. Rosie had run straight home without looking back, she told us. Never in her life had she been so afraid. Talking all at once we recounted to her what we'd seen. Strangely, or perhaps unsurprisingly, we had all conjured a slightly different image. But we'd all seen something, of that we were certain.

Slower runners stumbled in, red faced, relieved. But where was Nick?

We waited. We worried. We invented scenarios. Then as the minutes ticked by and our heartbeats returned to normal we began to laugh. What fun that had been! Had we really seen anything at all? Of course, Nick did this every week. The whole thing was a set-up, a bit of fun, a team-building exercise. But what about the dog? Well, she was probably bored of the game. She had simply had enough, and taken herself home.

We climbed into bed exhilarated, exhausted, safe.

Twelve teenage girls bounced down the stairs for breakfast, still chattering about the hilarious experience they'd had the night before, and how cleverly Nick had played them, making it seem so real that none of them had even reached the supposedly haunted stream. I felt a bit uneasy. I wasn't easily fooled and I still believed I'd seen a shape of some kind. And I knew Rosie. I had seen her quiver. I said nothing, until Nick appeared. He looked as if he hadn't slept a wink, and we stared at him. Then we began teasing him. Had he managed to scare himself with his own stories? Where HAD he got to last night after we had left him there? Nick was an expert at keeping a straight face. Gathered around a camp fire he could have made us believe an apple was an orange. This morning, though, he was visibly different. Shaken, even. He had chuckled to himself, he told us, when we had all taken off running. He had succeeded in feeding our fertile and willing imaginations, leading us to a dark and spooky place where he could present us with his visions. Mission accomplished, he lit a cigarette and leaned back against the stone wall, enjoying the peaceful sounds of a Cornish summer evening. The hairs on his neck made him look up in time to see a dark shape moving towards him. He stood upright and dropped his cigarette as the shadowy figure came closer and closer until it passed right through him. He felt an icy cold before he, too, sprinted home. We needed to know everything...what exactly did it look like, this shape? It was unclear, he said. There was no moonlight, it had approached him in darkness but the one thing he could make out was a yoke across its shoulders, some kind of pail on each end. Something on its head.

I have often been accused of living on 'Planet Mary', as if it is, in some way, foolish to dream, or to believe in a better future. I suppose I escape there. It's the place where everything I see as wrong with this world is miraculously absent. Evil, abuse and environmental degredation simply don't exist there.

In the past, close friends have rolled their eyes during my rants, dismissing them as the idealistic ramblings of an inhabitant of Planet Mary. Or, should I say, THE inhabitant, since I apparently live there alone.

In truth, Planet Mary is not floating around our solar system in a detached way. It is here on Earth, a paradise of my own imagination and self-protective optimism.

If there were, indeed, a separate planet for each of us and we could design our world just as we chose, I would start with what we have already. I would replicate our own Earth with its unsurpassable, magnificent and diverse beauty.

I'd empty it of all human beings and all human creations and endeavours. I'd recreate all the species ever to become extinct as a result of human existence. When my new old planet was as perfect as I could make it, I'd reintroduce indiginous peoples, living in harmony within their environment. Eventually I'd allow a sustainable number of like-minded individuals to follow lives of their choosing, building societies and civilisations faithful to their way of living, though adhering to strict criteria:

No woman would ever give birth to more than two children, and she would not become fertile until she was in her late thirties. Thus, the human population would never grow to a point where the ecosystem would be in peril. All construction, agriculture and transport would be completely sustainable. Travel and cultural interaction would be viewed as healthy and desirable with mutual respect and interest between all races and cultures.

If I were to delve into pure fantasy, we'd be able to travel anywhere instantly on an emissions-free magic carpet.

Societies would be equal and fair, where everyone's unique talents and abilities would be harnessed, respected and nurtured for the benefit of both the individual and the society in general.

Nothing would ever be worshipped besides the Nature upon which we all depend.

As balance would have been restored to the planet and all debris and pollution cleared, the climate would have returned to its natural cycles. While understanding that over millenia all life will eventually cease to exist, the changes will be slow, gradual and scarcely noticeable for the new citizens of Planet Mary who live simply, peacefully in contented fulfilment.