It is easy to miss it as you drive along the winding road from the picturesque Snowdonia village of Capel Curig to the Pass of Llanberis. But if you look up towards the right-hand side of this beautiful glaciated valley, you will spot, high on a ledge halfway up the mountainside, a clump of mature trees sheltering the farm of Dyffryn Mymbyr.
This is no ordinary Welsh hill farm. It was the place where Thomas Firbank wrote his best-selling book I Bought a Mountain in the 1930s – one of the first examples of the rural-escapism genre that became so popular in the late 20th century.
Sheep, rain and dogged determination feature large in the stunningly rugged landscape of the book. Firbank's adventures more than 70 years ago – whether it was his attempts to introduce pig rearing, to sell beverages to passing walkers or to grow carrots in the waterlogged soil – proved to be endlessly fascinating for his largely urban readership. But perhaps his most impressive "idea", as he called it, was to introduce a hydroelectric scheme that would power the lights, heating and coveted electric cooker of Dyffryn Mymbyr in the days before such remote farmhouses were linked to the national grid.
Hefted sheep, which have for generations roamed freely yet do not stray far from their home turf, have weaved the grassy texture of this landscape. They were also Firbank's main livelihood. But he was always on the lookout for other ways to supplement his meagre income, which led him to experiment with some rather unusual "ideas".
Rain and water are as integral to Snowdonia as are mountains, a fact that Firbank wanted to exploit to his and his wife Esmé's advantage. "We were used to seeing the valley change from lazy placidity to maelstrom of conflicting elements. Dry gullies would become streams in a few minutes, streams rivers, and rivers lakes. For Dyffryn has seven times the rainfall of London, and four times that of Betws-y-Coed, six miles away," Firbank wrote.
So he decided to use a natural plateau set into the hillside just above the farmhouse as the site for a small reservoir to collect water from the many streams rushing down. From this man-made pool of water he ran a pipe 300ft down the mountain to a stone-and-slate shed housing a hydroelectric set. In this small outbuilding, Firbank's dynamo transformed the movement of rushing water into electrical power, an early example of the in-situ "micro-generation" of energy that is all the rage among environmentalists today. The shed and its hydroelectric apparatus still exist, with the equipment marked with the year of its installation: 1937.
Higher up on the Glyderau hillside, which forms the northern boundary of Dyffryn, the dried bed of the artificial lake is still visible, as are the two slate and sphagnum-moss embankments that Firbank and his men laboriously built by hand over one wet and bitterly cold winter to contain the reservoir's water. The hydroelectric set has long since ceased to generate current, but it is easy to imagine it working flat-out, with water from the high-pressure pipe gushing through the shed, a testament to Firbank's ambitious far-sightedness in spotting the energetic potential of the natural landscape he loved so much.
Today, Dyffryn Mymbyr is owned by the National Trust, having been donated by the family following the death of Esmé and her second husband, Peter Kirby. The trust has tastefully renovated both the medieval farmhouse at the rear of the farm complex – one of the oldest buildings in the neighbourhood – and the much larger 19th-century farmhouse to the front, with its splendid views over the U-shaped valley and the twin glacial Llynnau Mymbyr lakes joined by the meandering Nant y Gwryd river.
Both properties opened as holiday accommodation this year. The older building, with its two bedrooms, is still in the style of a 17th-century Welsh farmhouse, with massive wooden beams and stone floors. The newer farmhouse, with four large bedrooms, has been renovated in a more retro 1950s style, in keeping with its recent history. From the window of the huge farm kitchen, there is a splendid view of the summits of Snowdon. On a sunny day, it is possible to eat outside on the farm's front terrace overlooking the valley, an uncannily Alpine experience.
Dyffryn Mymbyr is a key part of the National Trust's ambitious plans to generate more electricity in Wales than it uses. The trust is planning to renovate Firbank's hydroelectric scheme as part of its wider initiative to install similar water-power projects on several sites across Snowdonia, which is blessed with the densest concentration of high-altitude water in Britain.
"It's no coincidence that the hydroelectric scheme built by Thomas Firbank when he lived in Dyffryn Mymbyr has influenced the hydroelectric work the Trust is now undertaking in the valleys surrounding his farm," says John Morgan, assistant director of the National Trust in Wales.
With all this talk of record-breaking rainfall and torrents of water, it would be easy to be put off visiting this exquisite area of North Wales. In fact, for the few days we spent there the weather was on perfect behaviour. Crickets sang in the grassy, ungrazed meadow to the front of the farmhouse where Esmé once grew her flowers, and bees lazily drank on the nectar offered by the platoons of foxgloves standing rigidly to attention on the surrounding hillside. In the distance, a few wispy clouds of mist – the breath of the Welsh dragon – blew over the summit of Snowdon as we sipped chilled wine in the warm sunshine bathing Dyffryn's front terrace. And from the verdant valley below, a cuckoo called mournfully from another clump of trees sheltering a distant hill farm.
It was a world away from the wet and windswept winter's night eight decades ago when Thomas Firbank first went inside his beloved farmhouse, the place that inspired his vision of turning the energy of running water into electric power.
Dyffryn Mymbyr Farmhouse sleeps eight and costs from £658 per week. The Dyffryn Mymbyr cottage sleeps four and costs from £435 per week. Both are also available for short breaks. Book on 0844 800 2070 or at nationaltrustcottages.co.uk