This region is a slate graveyard; you can barely move for piles of the stuff. In the late-nineteenth and early-twentieth century, north Wales was the slate-mining heartland of the country. The longest underground zipline in the world lies here, in the blackness, deep down in one of these mines. It’s part of a 5km network of nine ziplines only accessible via several traverses, scrambles, climbs and abseils. You enter the blackness for fun, wondering what level of hell the miners endured for most of their short lives, and at some point you stand in the deepest publicly accessible point in Britain, nearly 400m below the surface.

“You enter the blackness for fun, wondering what level of hell the miners endured for most of their short lives…”

Back above ground, 20km away, the world’s fastest zipline, Velocity, flies people high over the mounds of grey slate, whizzing passengers across at an incredible maximum speed of 190kmph, equivalent to a belly-to-earth skydiver’s terminal velocity.

I decide to warm up with Velocity. My excitement levels have risen dramatically, and I’m all in. It’s run by ZipWorld, a steadily expanding giant-adventure-playground empire. They operate a range of ziplining and adventure courses, but Velocity is the main event, what with its world-record-holding speed limit. The vertical drop is over 200m, and at 1.6km the line is the longest in Europe.

The following day before heading to my next ziplining gig, I make a quick to detour to another ZipWorld base at Betws-y-Coed. For a tenner, you can hurl yourself off the top of a 31m tree and plummet to the ground, attached to a chord with powerfan technology that allows you to simulate the feeling of a skydive freefall, slowing you down before you land. The tree looks nauseatingly tall. I’m not generally afraid of heights, and I’m usually the annoying one elbowing to the front of the queue when the opportunity for an adrenaline-pumped activity arises. But this simple lanky tree, practically in the middle of the car park, has unnerved me.

I steadily climb up the trunk using the handy metal stirrups, making absolutely sure not to look down. I’m clipped in at the top and before I know it my toes are over the edge and I’m stepping off, absolutely petrified that I’m going to die a horrible death in a messy heap on the car-park floor below. A few seconds later, I’m still alive, in one piece, and ecstatically high on the rush. The fall wasn’t stomach wrenching, as I had imagined, instead it felt rather floaty.

“At Velocity, there was a café, glossy posters and billboards, loads of people milling around…here feels like the middle of nowhere…”

Still elated, I pull into another a car park for my final nerve trial. I’m near the historic mining town of Blaenau Ffestiniog for the Go Below Ultimate Xtreme underground ziplining adventure. At Velocity, there was a café, glossy posters and billboards, loads of people milling around, a cosy reception, children playing and dozens of staff. They funnel groups of ten people through every twenty minutes. Here, it’s a rather different story. It feels like the middle of nowhere. There’s no office or on-site café, just a flimsy sign, a rickety equipment shed, two trip leaders and a group of seven lads, one of whom is being sick. It transpires that I’ll be spending the rest of the day down a mine with a viciously hungover stag group. If I was apprehensive before, I’m full-blown anxious now.

Ewan and Duncan, our guides for the day, give us a warm welcome, kit us up with helmets, harnesses, wellies and head torches, and we march uphill for half an hour or so, through a quiet hamlet and past a pretty lake, while Ewan makes a continuous string of terrible jokes. Fortunately, he’s pretty serious about mines. “I spend most of my time underground; I’m a caving instructor, too, but I prefer the mines. There’s so much to explore down here – today we’ll only see the tip of the iceberg.”

When we’re anywhere near a drop (which is most of the time), we’ll be attached by at least one of the cow’s tails, dangling karabiners, on our harnesses, which means we’ll never fall far. The boys have stopped chucking up, and we head into the abandoned mine.

“The boys have stopped chucking up, and we head into the abandoned mine.”

The first thing that hits me, before the darkness encloses us, is the damp cold. I layer up, and we tread carefully down slippery rail tracks, past an old crashed cart. I’m grateful that there aren’t any constricted, narrow tunnels to crawl through, so it rarely feels claustrophobic. Go Below have left things as much as possible as they are down here, they haven’t added lighting and sturdy bridges or extra platforms. However, they have added occasional extra ledges and iron rungs to help ascend steep rock faces, and, as you’d expect, safety cables and ropes are funnelled through hundreds of metal hooks, plus of course there are the nine ziplines.

Our first zip is the record-holding longest one, Goliath, at 130m – not that long by normal standards, but the angle is treacherously steep. It’s a comfy ride though, as it has a convenient seat contraption. Duncan test-rides it into the abyss, and hollers once he’s down. I can see his light bobbing around on the other side, and the drop below doesn’t seem too far. It’s fast and fun, much like a rewinding, speeded-up chairlift.

The Victorian miners had to pay for lighting themselves as well as safety gear, so they used to bring down their own candles. We all turn off our head torches for a couple of minutes to get a true sense of the blackness. It’s inky thick. Ewan explains that our eyes would never adjust to this darkness, because the rock doesn’t let any light rays through. Standard low-light night vision goggles would be useless down here, you’d only be able to use thermal imaging. “Having enough light was crucial for the miners’ survival. Run out of light, and they’d have had it.”

Boys as young as 9 or 10 were drafted into the mines to carry cartloads of slate up and down the shafts. The youngest and smallest of them were given the unenviable task of carrying boxes of gunpowder, while holding a candle. It seems utterly absurd now, but it followed a cruel logic back then: the boys were the most inexperienced, unskilled workers, and thus the most dispensable and replaceable.

Time seems to pass more quickly underground. Before I know it, we’ve been in there all day, almost seven hours. It’s time for the final challenge, the literal leap of faith: a 21m jump, attached to another freefall device. We line up uneasily. When my turn comes, I step forward expecting to see the others at the bottom, but the strange angle means all I see is, once again, blackness. Ewan passes me an elastic cord, clips me in and says, “Jump!” Before I can overthink it, I push off obediently for the second time that day and am surprised by the sudden feeling of dropping like a bullet, somehow more shocking than the treetop fall. The brake-system kicks in just before I reach the ground, bringing me to a smooth landing, my head buzzing.

As we emerge with big smiles into the fading daylight, the warmth feels like walking off an air-conditioned aeroplane into the tropics. The air smells good. It’s been a remarkable and very draining couple of days. It’s official: ziplining adventures can be wild, after all… especially if you throw a bit of freefall in.

To read the rest of Mpora’s Wild Issue head here 

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DO IT YOURSELF

• Trains from London Euston take just over three hours via Chester to Llandudno Junction, at the northern tip of Snowdonia National Park.
• Having a car to get around the different sites is a lot easier than relying on buses, and cheaper than taxis. Avis have a rental point at Llandudno Junction station.
• Stay overnight at the cosy Eagle’s Bunkhouse in the quaint village of Penmachno, near Betws-y-Coed, for £19 a head.
• Go Below Ultimate Xtreme costs £79 and takes all day; weekends book up fast, so plan in advance.
• Zipworld’s Velocity is at Bethesda; it costs £60 and takes 2 hours. Plummet is at Betws-y-coed; it costs £10 and takes about 10 minutes.