‘Do you think I’m going to be cold?” asks my friend Ellie as we navigate the winding roads of Mosedale, on the north-eastern reaches of the Lake District, while rain batters against the windscreen. It’s a fair question. Both the Met Office and Mountain Weather Information Service are clear – being in the Lakeland hills will not be pleasant this Friday night, due to a sudden cold and wet snap. But there’s another reason she’s asking. I’m taking her to stay in her first bothy – that’s a mountain shelter left open, year-round, for walkers, climbers and outdoor enthusiasts to use, free of charge, with no way to book.

Unlike mountain huts in other parts of Europe and the world, they weren’t built for this purpose. They are old buildings left to ruin in wild places – former coastguard lookouts, gamekeepers’ cottages, remote Highland schoolrooms – before the Mountain Bothies Association (MBA) began to maintain them, offering shelter in a storm. And during this particular storm, shelter is definitely needed.

Before we left, Ellie was worried about what to pack, and well she might be. Despite a bothy having four walls, a roof, windows and a front door (they range from tiny, one-room affairs to sprawling, multi-bedroom structures), they are still very basic. There is no running water (there’s usually a stream nearby for this), no toilet (each has a bothy spade so you can dig your own) and no electricity (tealights and a headtorch are a must), and the one we are heading to, Great Lingy Hut, doesn’t even have the usual bothy stove for warmth.

Yet it’s precisely for these reasons that I’ve chosen it to be Ellie’s first. I know that because of the bad weather it’s unlikely we’ll have to share with anyone else. We park at the base of Carrock Fell, where the River Caldew is now a raging torrent. It is past dusk; the rain has eased to a mere mizzle and we can just make out the shape of the building on the skyline. With backpacks shouldered we begin uphill, keeping our eyes open for signs of walkers who may have potentially beaten us to it.

“Visitor numbers have definitely gone up in recent years,” the chair of the MBA, Simon Birch, tells me when I speak to him the night before. “Of course, back in the day they were kept a secret – some old documents I was going through have ‘confidential’ written across them. But people can’t keep secrets like this.”

It was in 2009 that the MBA decided to publish grid references to its 100-strong network on its website – despite some internal protests. After that, the “cat was out of the bag”, says Birch. When the MBA celebrated its 50-year anniversary in 2015, I asked and was granted permission to write the first guidebook about bothies – as a love letter to them, rather than a definitive guide. There was a lot of pushback, though. When The Book of the Bothy was published, I experienced online trolling (from MBA members and others), abusive emails, complaints to my publisher and even threats. But at the same time, one of the MBA’s co-founders, Betty Heath, told me how much she loved my passion; Birch told me that younger members began to sign up (when there was a real danger of membership ageing out); and now there is even a female thirtysomething trustee.

Out of the 105 bothies they currently look after, only two are owned by the MBA. All the others are on leases. “Ultimately, we could lose all our bothies, if the owners decided to take them back,” says Birch – which proves just how special the network and ethos of bothies is.

The hut we head to in the Lakes was originally used by miners at the nearby and now disused Carrock Mine (which dates back to the 16th century). It was relocated to its higher location on the moor as a shooting box. During the 1960s it was leased to the “Friends” Quaker boarding school in Wigton as an outdoor base and was fitted with a sleeping platform. When that school closed in 1984, it became an open shelter, and eventually the Lake District national park took responsibility for its maintenance before handing it over to the MBA in 2017.

We pass the mine workings under a starry sky, so they appear only as silhouettes. We ford the stream with the help of walking poles and mutual words of encouragement. Finally, we reach the door and experience the anticipatory few seconds that anyone who’s ever stayed in a bothy will know – when after hours of walking you knock on the door with mild trepidation, to discover if anyone else has beaten you to it. The door swings open. It’s empty. We have it to ourselves.

“The biggest change has been the impact that the growing popularity of long-distance trails has had on the bothies,” Simon tells me. “Some of the spots are incredibly well used, and we now have a sanitation officer in the MBA.”

I give Ellie a brief rundown of bothy etiquette. Put candles and the camping stove in the designated area so as not to cause a fire risk. Use the spade for the toilet – well away from the building and any watercourses. Set up a bag for waste. As a countryside girl, she has a good idea of the code – but Birch says a problem the MBA is facing in its 60th year is that content creators are showing people the bothies on social media but not teaching good practice. As such, in a very modern move, the MBA is seeking creators to collaborate with it, to demonstrate responsible bothying.

We settle in, heating a pre-made tagine and making hot chocolates to keep us warm. I also fill hot-water bottles. We chat for hours, me regaling Ellie with stories of previous bothy visits – including the time I inadvertently crashed a stag party in Scotland.

The wind whistles through the cables that hold Great Lingy Hut down, but despite this, as mothers of young children, we both sleep well away from the madness of our day-to-day lives.

Recent figures put the MBA membership at 3,800 – with many more users who don’t pay the annual £25 donation to join. We’re staying at one of the newer buildings in the network, but Birch tells me there are no plans to take on any more.

We enjoy our breakfast beside the window, where a lifting fog offers tantalising views down this little-visited valley.

As we leave, I feel hopeful for the next 60 years of bothies in Britain. We pack not only our own rubbish but empty packets and used candle holders left by others. “I love it,” says Ellie, “leaving it better than we arrived.” She may have begun this adventure worried about feeling cold but, thanks to the magic of bothies, is leaving as many do, warmed by the whole wild and wonderful experience.

For more information visit the Mountain Bothies Association. The Book of the Bothy by Phoebe Smith is available for £12.95 from guardianbookshop.com