The first bit was easy, and the territory well-known. The banks of The River were wide, smooth and flat here; on the left bank was a gentle rise, leading to a hill on which grew Standing Stones (probably an old sheep-pen) and mushrooms, which, come autumn, they would gather by the carrier-bagful, gingerly testing them for toxicity with the aid of Roger Phillips' "Fungi of the British Isles" and robust, youthful constitutions. To their right were cows, miring up the shallows as they waded in for their first drink of the day, sullen, steaming, untrustworthy. Also to the right lay flood-meadows, inhabited in spring by a myriad shrill and slippery amphibians, whose teeming children would be routinely kidnapped and kept in garden, outhouse, and pails of thick green slime, until, having swallowed the tails of their infancy, they should sprout unlikely limbs with which to climb the walls of their nursery prisons, and hop away.
For several miles, the stream remained easy to track, straighter than the road occasionally carried across it on low stone bridges. Here and there, too, a little footbridge joined one bit of pasture to its brother on the opposing bank, though it was shallow enough in most places to be easily forded by a sheep, or a toddler in red wellingtons.
A little further on, things started to get harder. The banks were steeper, the stream faster and deeper, and dense thickets of bramble and hawthorn in some places touched twiggy fingers above the waterboatmen and the snapping dragonfly larvae, in an arc so stooping that the three children now had to wade single-file in the rushing centre of the current.
Now they remembered the leeches. They knew, theoretically, that one could detach them with the help of a lighted cigarette, but no-one had thought how feasible it would be to light up whilst waist deep in black, leech infested water, which was undoubtedly already seeping into the rusty tin which contained their optimistic first aid kit, and a few ready-rolled tubes. Nor did any one trust the others to apply the necessary glow so close to their skin; but a bankside inspection at the next disembarkable spot revealed no hangers-on, so they were spared the painful proof.
By this time, they were feeling hungry, and thirsty too - who brings water to a watercourse? But they knew better than to drink from the River itself - not they! Water that was fast flowing over rock, on the other hand, was believed by all the children to be safe and pure, so when they came to the place where a mountain spring - naturally named The Waterfall - spattered down towards them, they took a brief diversion, climbing to the large flat rock at the clifftop to satisfy thirst, and view as much as they could see of their remaining itinerary. Here they also ate poor, unbuttered sandwiches, and set out three cigarettes to dry in the grass that was speckled with sundews, yellow tormentil, and dried sheep-droppings, which they flicked hilariously at each other with their sandwich-free hands.
From this point, the gradient started to climb. The river itself, of course, was actually rushing downwards, but we have to remember that the children were going the other way. It wasn't deep - the tallest child could walk along the riverbed near the bank without getting wet above the top of his boots, though the other two shipped water at every step like dwarfs hauling soft-sided buckets.
But although not deep, it was much faster now, and the stones on the bottom were slimy and treacherous, so they found themselves rapidly tiring. They had loitered at The Waterfall for longer than they had intended; the sun had already fallen away behind the grey, bare mountains ahead of them, and great clouds of gnats appeared, diving en masse with joyful whines to feed on sunburned necks and arms.
Still, no-one was ready to admit that they wanted to stop; so they carried on, rather slower, and much more ill-tempered. They passed the massive crag called Ifan's Head, but didn't see the eagle. They wondered if Farmer Jones had shot it, as he had threatened to do; which, if it were so, they considered a selfish and hypocritical act. Jones left his flock out year round on the mountainside, uncounted and uncared for, to live or die as suited themselves - what was a lamb more or less to him, when Subsidies took care of the rest?
Now it was dark, and they were cold, and hungry again. They had intended to pad out the sandwiches with blackberries, and bilberries, perhaps, but those were still, at midsummer, hard, and green.
For a while they rested up against a solid clump of cottongrass, sucking cucumber-flavoured reeds to confound their hunger, and arguing. Two wanted to go back; it was after dark, and they would be in trouble. One thought they should go on; they were already in trouble, and they still hadn't reached the Source; they would be punished, and they would also have failed.
The argument was abruptly halted by a noise. Something was coming towards them through the bracken on the far bank. Something big. A sheep? A dog... a panther! There was a panther, living wild above the treeline. Everyone knew it. It had eaten three cats, and a sick ewe, and once it had chased Mog Edwards all the way home from the pub, though that probably wasn't true.
The three scrabbled up to the road as fast as waterlogged wellies would allow. The road was almost worse, gleaming dully back down the valley like the trail of a vampire snail, emptier than the coldest, loneliest lunar landscape.
Then they staggered, stumbled, and ran as hard as they could, shoving one another towards the ditch in echoing, hollow bravado, crying not to be left behind, and hearing Footsteps, padding surely and rhythmically behind them, until at last, clammy, wheezing, heart-thumping hours later, they passed the safehouse of the first orange street-lamp and dispersed to their respective homes, too late for dinner, too late for bedtime, too late for any reasonable explanation.
And the map?
They had left it behind. For all I know, it's still there.