Going Underground: Inside Roni Size’s Record-Breaking Rave Beneath a Welsh Mountain

“Welcome to the most miserable town in Wales!” our taxi driver declares with sarcastic enthusiasm as we pass through the tiny village of Capel Curig. He’s not talking about the locals, or its crime or poverty figures. He’s talking about the weather. With more than 2,700mm of rain in a typical year, this corner of Snowdonia frequently earns the dubious distinction of being the wettest place not just in Wales, but in the entire UK. Lucky for us, we’re getting the authentic experience: it’s raining cathod a chŵn.

We’re less than five miles out from our destination, Cwmorthin Slate Mine, part of a vast underground mining complex once considered the largest of its kind in the world. Deep beneath the mountain, drum-and-bass pioneer Roni Size is teaming up with G-SHOCK to attempt a record of a very different kind: the world’s deepest underground rave, 1,375 feet below the surface. Joining the descent are just five competition winners, selected at random from more than 4,000 entrants for the chance to witness it in person. For everyone else, G-SHOCK is streaming the set to the surface and beyond via its Mixcloud radio station.

We’re dropped off at the headquarters of Go Below, the adventure company that will be guiding us into the mine. Until now, we’ve been kept largely in the dark about what to expect. The feverish social media speculation in the run-up hasn’t exactly helped, with some outlets billing it as a “huge” free-party-style rave and others questioning whether the sound system’s high frequencies might trigger a rockfall, potentially laying the foundations for the next instalment of Netflix’s Trainwreck series.

Given the logistics, not to mention the health and safety implications, the prospect of hundreds of gurning ravers stumbling through a slate mine without protective gear was obviously never going to be green-lit by anyone with more than half a brain cell. That said, when I’m picked up from Llandudno Junction alongside a fellow journalist and one of the competition winners, none of us can quite picture what we’ve signed up for.

As the adventure draws closer, the inimitable words of Danny Dyer in The Real Football Factories begin echoing around my head: “What have I got meself into? I am fucking shitting meself. I can’t back out now.” Then again, he made a pretty convincing case for raving in Human Traffic. Onwards we go.

We’re driven to the mine entrance by Nick, one of Go Below’s senior mine leaders, who finally fills us in on what’s actually happening. Slate, he explains, absorbs sound very differently to other rock. For the music to have any chance of causing a shift or collapse, the system would need to be pushing more than 140 decibels, at which point, he jokes, we’d all be vaporised anyway. The fact that tonight’s volume is capped at 85 dB puts us somewhat more at ease.

Along the way, he talks us through Cwmorthin’s history. The quarry opened in 1810, extracting slate destined largely for the roofs of Britain’s rapidly expanding towns and cities. It was acquired by the neighbouring Oakeley quarry nearly a century later, after which the two were connected underground. Both eventually closed in the 1970s, although small-scale operations continued until 1997. After the mine sat largely untouched for more than a decade, Go Below acquired a lease and began leading expeditions into its sprawling network of tunnels and chambers. In 2023, it opened Deep Sleep, giving members of the public the chance to spend the night underground in wooden cabins equipped with electricity, internet access, toilets and even a bar.

With that infrastructure already in place, plus the guides and underground expertise to go with it, Go Below was an obvious partner when G-SHOCK approached the company just four weeks ago with an idea: stage a record-breaking rave deep inside the mountain to launch its new MUDMAN, the GWG-B1000.

The idea was one thing. Making it happen was another.

The official record for the deepest live music performance was set in 2024 at a base-metal mine in Ontario, Canada, more than 9,000 feet below the surface. But there was one rather significant advantage: they had a lift. At Cwmorthin, there’s no such luxury. Everything has to go down the same way we do: on foot. For the past 48 hours, a team of 18 has been hauling everything needed for the show through the mine in heavy rucksacks, reaching the chamber before turning around, climbing back to the surface and doing it all over again. Sound equipment, lighting, cameras, batteries: if it’s going to be used 1,375 feet underground, somebody has to carry it there.

At a cottage not far from the mouth of the mine, we’re kitted out with helmets, wellies and harnesses before being given a brief health and safety talk. The main takeaway is simple: if you get lost, sit down and wait to be rescued. Cwmorthin is a labyrinth of hundreds of tunnels and passageways spread across 12 levels, so this is no place for misplaced bravery. Wander off and assume you’ll eventually loop back round to the group, we’re warned, and there’s every chance you’ll only succeed in getting yourself even more lost.

With that comforting thought ringing in our ears, we switch on our head torches and follow our guide, Chris, into the darkness.

Past rusting, derailed mine carts abandoned in the darkness, we reach our first real obstacle: a 30-metre vertical drop. One by one, we clip onto the rope and abseil into the unknown.

Once reunited at the bottom, there’s little respite. Reaching the next chamber means edging along a narrow steel pipe, one hand gripping a chain bolted into the wall as we shuffle above the freezing water below. Lose your footing and you’re getting drenched, which is not an especially appealing prospect when the temperature down here is already struggling to reach double figures.

Along the way, Warren Halliwell, one of G-SHOCK’s senior marketing figures, stops to share a few facts about the new watch and the lengths the brand goes to in demonstrating the durability of its products. Suffice to say, this isn’t your average marketing job, sitting around a boardroom discussing which TikTok dance to jump on next. Over the years, Halliwell’s work has taken him from the jungles of Southeast Asia to the wilds of Sierra Leone, working alongside armed and special forces to put military-grade G-SHOCK watches through their paces in some seriously unforgiving environments.

Our guide, Chris, also gives us a crash course in how the slate was once extracted. In one chamber, he picks up a jumper bar, a long, brutally heavy steel pole that miners would repeatedly drive into the rock, turning it between strikes to gradually bore a hole. It was painstaking work, with a single hole taking as long as seven hours to complete. Once deep enough, it would be packed with gunpowder and prepared for blasting. The job of lighting the fuse, Chris tells us, sometimes fell to children, whose smaller, more agile frames gave them a better chance of scrambling clear before the charge went off.

After a zipline and a steep scramble down a miner’s staircase, the first faint thud of bass begins to pulse through the darkness, growing louder with every step. Finally, we reach our destination. After almost two hours underground, it feels surreal enough to encounter other people, let alone find them dancing as G-SHOCK Radio’s own DJ Nav warms up the crew who have spent hours down here getting everything ready.

We’re greeted with a case of chilled soft drinks. No booze, for obvious reasons. The makeshift venue occupies a vast chamber with a ceiling that disappears into the darkness above, while the dancefloor itself is a narrow strip of ground wedged between a body of water and a precipitous drop. On it, a huddle of twenty-something ravers in matching blue hard hats are already throwing shapes. Before Roni steps up to the decks, the Welsh national anthem rings out through the chamber to mark the occasion.

The Bristol drum-and-bass legend opens with something altogether more atmospheric, an ethereal track built around a spoken-word sample celebrating the cultural achievements of his home city and its importance as a breeding ground for DIY music and art. It feels like a fitting introduction from someone who has spent more than three decades at the heart of that culture.

And then, bang. For the next hour, it’s limbs, gun fingers and every conceivable variety of skanking as the chamber comes alive for a party that nobody here is likely to experience again. For those of us who have only just arrived, bewilderment is probably the overriding emotion. For the crew who have spent the past two days hauling equipment down here and turning a cavern deep beneath a Welsh mountain into a functioning nightclub, it’s pure euphoria. Roni delivers, the crowd responds, and somehow G-SHOCK and Go Below have pulled the whole ridiculous thing off.

Eventually, it’s time to make our way back up. If the descent was tough, the return journey is considerably less forgiving on the legs. By the time we finally emerge from the mouth of the mine, the last of the daylight is struggling through a thick blanket of fog. The rain starts hammering down again as we follow the dirt track away from Cwmorthin, still trying to make sense of what we’ve just experienced.

Later that evening, sitting in a nearby pub, someone asks me: “So, what’s the craziest gig you’ve ever been to, then?”

I think you know the answer.

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Listen to Roni Size's set via MixCloud below.