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Croesor Rhosydd

Deep into North Wales' slate mines

The Croesor - Rhosydd through trip is a well established route within the British mine exploring community and one I was lucky enough to take recently. Through a work connection I was invited to attend with a group of dedicated Yorkshire cavers. It's absolutely bonkers.

Into the slate mine, wales.

The Croesor and Rhosydd slate quarries were established in the early-mid 1800s and separately worked through until about 1930, shipping an esimated 20,000+ tonnes of finished slate between them. These two quarries are so close that both launched legal proceedings claiming the other was infringing on their respective boundaries. After investigation they discovered both were guilty and eventually connection between the two created. Management quickly clued on that workers were using this connection to sneak off shift early via the other mine. They sealed it up quick smart. Today the connection is open once more, allowing the intrepid explorer to typically enter the mine from Croesor, pass through the mountain's belly, then exit via Rhosydd on the other side.

Down in the deep below the mountain things take on epic proportions. The large slanted chambers cut to match the geological formation of the slate are truly colossal, vanishing into darkness far beyond the beams of our lights. The levels in the mine are stacked parallel to each other but angled into the ground at approximately 30 degrees. The tracks running throughout the level are all flat however, creating a situation where large angled shafts run through what used to be access/haulage tunnels into the bottom of the shaft. To keep these tunnels connected to working faces which had not yet dug below the tunnel level huge wooden beams were suspended from the room over the shaft voids creating neat bridges. These old bridges now account for much of the challenge and consequent enjoyment the through trip provides. They're no longer in the safest condition.

First pitch inside the Croesor slat emine. The rocks to the right of frame, were once in the roof. Notice figures in the lower center for a little scale.

We quickly reached the first pitch, of 80ft. All the pitches and obstacles are already bolted and rigged though it's prudent of course to check everything. In this case the rope rigged on the first pitch was in reasonable condition but a couple of metres short of the landing. The first chamber is of considerable note, being the riskiest of the mine. It's quite unstable and the guys told me a few years ago a section the size of a house dropped from the ceiling almost killing a group. Apparently they just stopped there and waited to be rescued. I know old-timers like to mess with relative mine noobs like myself but as I abseiled into the chamber as quietly as possible I looked around and realised they were entirely fucking seriously. I could see the hole in the roof and the pile of smashed slate below it. I crossed the chamber quickly gribbing all my harness hardware tightly to prevent any rogue clinking.

Another short pitch leads into a small underground lake over which someone has affixed a wire zipline. The bolts looked good so we slung on the pulley and flew across. The landing area curves around into another lake which once held an more recently installed suspension bridge. The shiny cables and treads are clearly visible though the clear blue water, resting peacefully on the bottom. I feel for the poor soul who rode that puppy down. One concept I was introduced to on this trip was 'float'. Typically this is simply 5-10L of empty plastic containers clipped on, to prevent your pvc oversuit, wellies and SRT hardware dragging you to your watery grave. In a place like Croesor that could be deep. Bring a boat, you'll need it here.

Beyond the first lakes we encountered the bridges I mentioned earlier which cut across the middle of several large water filled chambers. Originally these chambers were working faces. The workers would take a chain bolted into the wall, wrap it around their leg and keep their hands free to cut and drill the slate. In some places these bolts and chains are still visible. Some of the bridges are gone entirely, replaced with bolted ziplines. Others are far scarier.

photo from wikipedia

The final bridge, affectionately named the Bridge O' Doom is merely two rusty slivers of railway track laid from the near edge of the chamber onto a rotting chunk of timber. It's suspended by two rusty iron rods bolted into the slate ceiling. Stretching from the chunk of timber to the other side is a taught wire cable just out of reach. You climb up one of the rods, clip on and haul yourself across. If you're lucky and someone else went before you they can reel your tired, sorry ass across.

Rhosydd Tracks

The last obstacle of the mine is 40m boat ride across the biggest underground lake I've seen. Boarding your poor inflatable vessel is an adventure in itself, since it's a sheer 10m drop into the lake. The recommended method is to dangle your pack between your legs like an oversized nutsuck, hover your ass above the boats, spread your legs and drop in. If you're the last to cross and your oversuit has seen better days then you'll surely have a wet arse but the vast chamber is so impressive you'll soon forget. The chamber disappears around to the right leading to the small landing site.

Intrepid explorers in large ore chamber. Welsh slate mine.

After beaching your boat a short ascent leads into the final 2km hike which, via more vast ore chambers, finally spits you out of the mountain wet, exhausted and reborn into a hardened mine explorer. Approximate through trip time: 7-8 hours. The risks are serious, the environment unforgiving and the consequences of error severe. The ways to die in here are numerous - cave ins, downing, falling, hypothermia, getting lost, or any combination of the above. If you're not dissuaded already then good luck to you, this is a spectacular and rewarding trip.

Exit from the Rhosydd slate mine.


On 22nd June 2009 Ian Bishop passed away after his long battle with the tumor. He'd been diagnosed in early 2007, Ian was dying and he knew it. Far from lying down and giving up he attacked life with vigor and enthusiasm far greater than that of the tumor which did the same to him. He seized his days and took to life in a manner in which we could all emulate, even if only a little. Rest in peace Ian.

Ian Bishop in the Croesor-Rhosydd slate mines in wales, 2008. One of the most eager and sincere people I ever had the luck to meet. Rest in peace Ian.

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