Inside there is a slate floor polished by two centuries of Welsh feet. In the rooms beyond we find a pair of log-burners, two cast-iron baths and several well-worn rugs and sofas. Best of all, there’s a kitchen humming with warmth from an Aga, a guitar and many piles of books. Later, I stand outside on the sheep-cropped lawn, watching the millstream cascade into a pool and think: “I’m getting under that … probably, at some point.” And: “This is perfect.”

If there are, as most reputable psychologists now accept, three types of human being – those who will never own a head torch, those who forgot to bring it, and those who wish they had one built into their forehead – then I put myself in the last category. I say this as a kind of full disclosure announcement. Garth Gell in Snowdonia (or Eryri), works for me. Off-grid, off-wifi and awfully far from the bright lights. There is, it turns out, actually a phone signal in the top corner of the bathroom, but I’m keeping that to myself.

Conjure up, in your mind’s eye, the perfect winter cottage. I know there are people, and I’m in close contact with some of them, who balk at the idea of a holiday that involves cooking their own food or washing up. Some even whisper affectionately about hot tubs, saunas, televisions with streaming channels (I guess it’s good to know what you like), but none of these are dealbreakers for me.

Walk around a town in Scandinavia in winter and peep through the windows. I remember doing that in Kristiansand, Norway, while I waited for the Newcastle ferry (there used to be one). Behind each frosty pane were advent candles revealing well-designed, largely wooden interiors, plus trays of sugared buns and coffee pots. Those images had a formative effect on my idea of what makes the perfect winter cottage.

At night outside Garth Gell, I can see one distant bulb. My partner, Sophie, confesses that arrival in such silent rural darkness always triggers irrational fears of mad axemen, a fear that I do my best to dispel, explaining that many brutal murders do not involve axes at all. We sit out on the stone bench under the stars. An owl hoots. Sophie begins to relax, but I don’t suggest a ghost story – another great addition in a winter cottage.

Once we have established that there is nothing to fear, the next requirement for a winter cottage is definitely warmth. An Aga has the advantage of always being on, so those annoying folk – and I’m one – who go through life opening windows and turning down thermostats are foiled. There is a slight planet-destroying aspect to all that oil-guzzling, but let’s not be pernickety: in this instance, without mains electricity, gas or water, the household CO2 emissions are definitely well below average. That one warm kitchen works when the room is attractive and comfortable, and this one is: a cushioned settle down one side, scrubbed large table and plates on a dresser. Best of all is that the slabs of floor slate were clearly cleaved at the same time as Stonehenge was built and have been absorbing heat ever since. I walk around barefoot.

Managing expectations with winter cottages is vital. An Aga and two log burners looks like belt and braces, but I have at times been misled by my own assumptions. When a friend offered to lend a cottage that was “idyllic and remote, and we are going to do it up”, I was so excited that I failed to register the all-important qualification, “going to do it up” and imagined my ideal: a cosy compilation of those Kristiansand homes and a forest cabin, where the mulled wine is warming on the range while outside the cold wind howls. My son and I trekked across the North York Moors in a snowstorm and arrived shivering to find a dodgy old kitchen range, draughty windows and a stock of damp firewood. We huddled in our sleeping bags round a faltering flame. The bottle of wine remained frozen solid.

If location and cosy warmth can be guaranteed, however, the next thing is to take a good look around the place. Somewhere inside that cottage, if it’s worth its salt, will be the key to forging fantastic memories. One glance inside Garth Gell is enough to know that such a key must exist inside. I bang out a few chords on the guitar, it’s not that; I read a couple of local guidebooks, no bells ring; I look through the pile of board games, nothing jumps out. So I take my head torch and search.

The trick is to be open-minded. Some years ago on a US road trip, we trekked out to a cabin in Montana’s Crazy Mountains. It was 19 miles from tarmac and 26 from the nearest shop, where they sold guns, ammunition and whistles that made duck noises. I asked the owner about bears. How best to deal with them? He eyed Sophie and our daughter, Maddy, critically. “Make sure that you ain’t the slowest runner.”

The mountain cabin was simple. In fact, the only luxury item was a battery-powered DVD player that had one disc in it, but we scorned such gadgetry, we were here for the complete backwoods experience, not Hollywood fakery. Maddy and I tried fly-fishing in the river and caught nothing. That night we played cards and next day we fished, failing miserably once again. After two more nights of cards, we gave in and watched the DVD. It was Robert Redford’s A River Runs Through It, a tale of fly fishing in the great American wilderness. In one scene the two heroes sneer at some hapless loser who fishes with worms. Next morning Maddy and I tried worms and caught three beautiful big trout for dinner. The key to great memories, you see, is up on that high shelf.

In Garth Gell I find lots of those two-and-sixpence Penguin novels whose orange spines always pull me in. Among them I spot The Treasure of the Sierra Madre, a 1927 adventure story by the mysterious Bruno Traven. I might have ignored this volume except for having just read in the notes that Garth Gell is built on top of Wales’s long-defunct gold seam. The Romans probably took the best of it, but there was a brief goldrush in the 1860s. I take down the book and am immediately hooked. Traven’s stark tale of the hunt for gold and its effect on his trio of characters (Humphrey Bogart plays the worst of them, Dobbs, in the classic 1948 film) becomes the mood music of my stay.

We hike uphill and inspect old mine workings. I search through piles of stones for lost nuggets, hissing, Gollum-like, “Come here, my precious”, then try panning in the river, inexplicably without success. Finally, we yomp to the top of Diffwys (750 metres), and at last strike pay dirt. There, stretched out below us is all the riches we could want, the hammered gold of the Mawddach estuary and the Irish Sea. We come down the ridge in gathering cloud, cross valleys where hidden streams gurgle, and finally spot our cottage. It looks, I have to say, just about perfect.