Snowdonia, Wales

The Chamber of Horrors

Date September 2008
Posted September 2010
Attempting the Croesor-Rhosydd Through Trip
The battering of rain on the windscreen was more than the wipers could deal with, great torrents of water flowing in lines down the glass. Four faces peered out into the gloom through misted windows, probably each wondering why we'd stubbornly decided to go regardless of the weather. Somewhere ahead of us was the farm track leading up to the old quarry site, way up on the bleak Snowdonian mountainside. If the car and the roads were awash, the hillsides were something else: streams and springs were swollen and from here up to where cloud enveloped the summit white raging cascades cut through the grassland.

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

The farm track made finding Croesor Quarry relatively easy despite the fact we were now walking up through the downpour, already sweating in caving suits and carrying plenty of gear. None of us had been into this notorious mine system before, and it's probably fair to say there's not that much else in the country quite like this trip. The entrance to the Croesor adit (or entrance tunnel) is nondescript, tucked away behind some topside ruins, but easily accessible. We ducked in through the small opening, feet crunching on slate producing that distinctive echo that's shared by all the underground quarries of this nature, and the clinking of rope gear.

Each man would require a harness, 'single rope technique' (SRT) kit for descending and ascending fixed ropes, and then whatever else he saw fit to carry (food, drink, first aid kit recommended). Initial doubts about going underground with so much water coming down from above were soon put to bed within my Petzl-protected skull, possible combinations of painful injuries and death scenarios gladly accepted. These prerequisites are the same for any who decide to embark upon the famous Croesor Rhosydd Through Trip (CRTT).

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

Reaching the remains of the furnace and the first incline our efforts turned to an easy upward scramble following the clay flue up to a passage on the left where suddenly a vast nothingness began. Once a bridge had started here that crossed the huge chamber indicated by the blackness. Less than half an hour into the quarry and we'd made it to the simply colossal Chamber 1 East. Torch beams picked out bits of slate here and there but mostly we were rewarded only with inky darkness. The treachery was to begin, but this was not down to the ropework which, to the distaste of some, is well installed and maintained. Instead the danger here is down to the fact that Chamber 1 East is a little volatile, particularly higher up where car-sized lumps of rock are prone to falling off the ceiling. The cavern was quarried out to such an extent that the roof could not support itself, causing the partial collapse of the chamber. The floor is made up of fallen rocks and those still left hanging above are liable to fall silently and without warning at any moment. It's advised therefore that noise is kept to a minimum.

Chamber 1 East is negotiated with both the initial descent and a second one further along, dropping you back to around the same level that you came in on before the incline. Since Croesor quarry drains at this level through the entrance adit, the water level remains more or less constant, acting as a reservoir for crystal clear mountain water. Through this water we looked now into inky darkness, for we had to cross the first of a number of flooded chambers. This first water crossing is by means of a steel cable zip-line stretched across the chamber onto which a pulley is attached and clipped to the caver's harness. Then, placing trust in the kit, you jump.

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

In case you're now wondering just what the quarrymen were up to, here's a little history... Mining at Croesor began in 1846, the first significant development being the connection of the quarry to the Croesor Tramway in 1864. This means of transporting slate connected the quarry to Porthmadog on the Welsh coast. Further improvements were seen during the 20th century with the manager Moses Kellow pioneering the use of electricity. Consequently Croesor was host to some of the first electrically powered narrow-gauge locomotives used to haul the tubs of mined slate out of the mine ready for preparation.

Next door the Rhosydd mine was the largest of its kind outside of the Ffestiniog group (so called because the Ffestiniog Railway was their primary means of moving slate away from the mines), consisting of 170 chambers on 14 floors. Similarly to Croesor the workings were connected by narrow-gauge railways with gravity powered inclines used to move the slate between levels. Working shifts were long and inevitably dangerous, with virtually all mining work taking place underground (rather than topside) from the early 1850s onwards.

Disputes raged between the two quarries as they accused each other of excavating in the other's territory. More accurate surveying was required and so a tunnel was bored between the two operations. This tunnel would also serve as an additional escape route, particularly useful when you consider that Croesor had only one entrance adit. At some point a wall was built across the tunnel to prevent miners from escaping early through the other mine. The wall allowed ventilation and could be quickly brought down in the event of an accident. This tunnel is very significant for the mine explorer: thanks to a hole knocked through it adventurous mine explorers can enter the Croesor adit, travel along the disused workings to the tunnel and then cross over into Rhosydd, finally leaving via one of several exits back out onto the mountainside.

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

The second flooded chamber we found literally meters after detaching from the zip-line. Once host to an elaborate suspension bridge, this one is now crossable by swimming or boat only. Knowing from research that a dinghi would be required we'd brought one with us, but on this occasion a half-deflated alternative was bobbing about midway across the chamber. Fortunately it was tethered to a long length of nylon rope and therefore easily recovered, air topped-up and made ready for the crossing. Getting into the thing was a little harder since the 'quayside' was sharp slate and there was a risk of tearing a big hole in the vessel which would surely sink it in seconds.

With two crossings completed we were now some way into the workings of the quarry and it wasn't surprising to find narrow gauge railway tracks, points and other debris. Apart from some offshoots and dead-ends investigated on two later trips, the path is more or less obvious through the subsequent chambers. Each is crossable via a walkway as this level is near the top of the chambers and as such no theatrics are required. Coming shortly though was what the passage is more-or-less famous for: 'the bridges'. And 'bridges' is declared in inverted commas for the simple reason that most of the 'bridges' aren't really bridges anymore.

Croesor Quarry, Snowdonia, Wales (2009) courtesy of

The first of these ancient crossings is probably the safest with two wooden beams to shuffle across, plus a safety line to clip into. The moisture has not been so kind to the woodwork and it won't stay around for ever. A little respect for the fragile structures is required, passing over them one at a time and not stamping about or being excessively heavy-footed.

It's at times like this that you have to keep your brain in gear. If you become lazy, complacent or slack then mistakes will be made. Rush the changing over of safety lines or decide you don't need them at all and you're risking a nasty death. In fact, even if the weight of your SRT kit and bag didn't pull you down it'd still be tough getting back up onto the 'A Floor' level from where you'd fallen. And then there's the minor problem of being stuck in the middle of the CRTT soaked through and no doubt a couple of hundred quids worth of kit lighter.

All four of us passed the bridge without any real difficulty and continued onward through several more chambers until reaching the second bridge. Continuing a downward trend this one had crumbled to little more than a single support hanging useless above the water.

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

The Petzl Tandems would again facilitate our crossing. These well-designed pulleys consist of two metal rollers mounted on bearings, both fitted into an alloy housing that covers the top of the line, therefore providing the necessary protection in the unlikely event of both spindles snapping. A good push off from the edge was enough, but be wary of striking the iron tie-bars that hold up the bridge support. Running out of steam midway is no problem as you can reach up to pull yourself along the wire, taking care not to run the pulley over your hands. For this to be possible you must ensure that you haven't rigged yourself so far below the pulley that you can't reach the line. Although in this case that's probably not an issue, as you'd already have ploughed into the bridge support.

From the second bridge there follows a series of easily passable chambers, one of which myself, northcave and MG chose to camp in on a second visit later the same month. To give ourselves enough time to explore the two quarries further we'd brought down additional supplies and the necessary kit to stay overnight. Despite the candles, inflatable mattresses and extra layers it was still cold. After consuming 'Hotcan' meals we tried to sleep, but it's difficult when the quietness is broken every now and then by the sound of a shard of slate detached from the ceiling of the chamber next door dropping into the water and serving to remind that we were deep inside the mountain.

Croesor Quarry, Snowdonia, Wales (2008) courtesy of

The following morning the third and so-called Bridge of Death looked no more inviting that it had the first time round. The remaining woodwork this time suspended from the ceiling by another somewhat decayed bridge support. A length of narrow-gauge rail and some ropes offer little safety, although a steel cable has been bolted into the wall for via-ferrata. This offers little consolation though as the whole lot shakes about with each crossing, it's integrity to remain a mystery until the day that it actually collapses into the oblivion below.

On the first trip through it was naturally even more surprising than second time around. Apart from some photos available on the web it was hard to accurately picture just what we might find at each stage. It did occur to all of us that should the bridge fail when one of us was clipped to part of it there'd be little room for anything other than a swift ride to the bottom.

Croesor Quarry, Snowdonia, Wales (2009) courtesy of

A short distance further and we arrived at the most notorious feature of the trip: The Chamber of Horrors. This, our final crossing of a part-flooded cavern, would once again call for the services of a boat. This enterprise however was a bit more serious, the chamber massive in size and from where we stood it was impossible to see where the crossing finished. Our view of the 'landing' was completely obscured by a huge slate pillar. At some point a simple but effective system of moving a boat across the black expanse of water had been set up: a continuous loop of nylon cord running around pulleys so that the boat wouldn't require rowing. Presumably this was done to allow kit to be shipped from one side of the other.

Pulling on the rope revealed that there was a boat already present, although from what we could see far below it's integrity was questionable. For the minute though the water was a secondary issue - before crossing this vast underground lake we first had to reach it from where the four of us stood, 10m higher up. The first to attach himself to the rope was stepping lightly, ensuring that his descender was backed up with a prussic knot to allow a controlled drop into the little boat. Before committing to the vessel though he reached down, lifted it up and topped up the air. Also provided with the boat was a small makeshift paddle in case of emergency.

Croesor Quarry, Snowdonia, Wales (2009) courtesy of

One by one the others departed across the lake, a distant shout indicating their arrival at the other end of the chamber. Finally my turn arrived and I prepared the descending device and checked for any kit that we might have left behind. Meanwhile the boat was being dragged via the pulley system back to the bottom of the small cliff atop which I stood. As with the first boat crossing a few hours earlier, the slate at the waters edge was characteristically brittle and sharp, and threatened to quietly but swiftly fillet the little ship.

At the bottom of the rope I followed my bag into the boat, trying to keep balance whilst pushing away from the rock and to the relative safety of the black depths. And like this began possibly the most serene moment of the trip, being slowly winched across a massive underground lake, free to admire the surroundings and, just for a few minutes, not having to concentrate on staying alive.

At the other end the boat reaches a small 'beach' and from here each person must undertake a short rope ascent into the continuation of A Floor.

Rhosydd Quarry, Snowdonia, Wales (2009) courtesy of

A short walk along the remaining Croesor passageways on this floor took us to that small wall where the two quarries were joined. Stepping over, we were now in Rhosydd. In place of tricky water crossings there was now a larger selection of workings and inclines and the possibility of getting lost. Still, the thought of returning back through Croesor didn't appeal by this time so it was onward and into the workings. On the so-called '4-6' incline which, as it's name suggests, connects floors 4 and 6, all of us agreed to stop to eat. At the top of this incline remains a large braking device used to control the cart moving quarried slate downwards under gravity. The cart itself can still be seen at the bottom of the incline whilst the counterweight is stranded halfway up.

A couple of moderate squeezes through rock falls separate the 4-6 incline from the giant 'Twll', a massive hole in the mountainside above providing a welcome beacon of salvation with light pouring down into the quarry. Reaching this point after a number of hours below ground was a breathtaking moment, not least because of the sheer size of the feature, illustrated in the photo below. The boulder-strewn chamber permits further passage underground, descending further via a series of inclines, or an upward exit through the Twll onto the mountainside. On this first trip we chose to exit through the Twll and face the rain up above, but a later trip and a separate visit to Rhosydd Quarry revealed a host of interesting features including the long 'number 9 adit' which exits on the otherside of the hill.

Rhosydd Quarry, Snowdonia, Wales (2008) courtesy of

The conclusion of an escapade such as this one is usually the most reflective point, each quietly thinking over the events that just took place. The danger has suddenly been lifted away and there is the realisation that on this particular day nobody met a nasty end. With it is a drop in adrenaline and energy levels as the threats faced are removed, these pyschological and physical responses coinciding with that euphoric feeling derived upon the successful completion of a risky venture.

At the top of the rocky exit the rain continued to pour down hard and after clambering up and into the air and cloud the four of us had to scramble up even further to leave the crater. From here a half hour walk would reunite us with the vehicle, warmth, food and, eventually, a beer.

Rhosydd Quarry, Snowdonia, Wales (2008) courtesy of

A big thankyou to Miles, vanoord and root at for all the helpful information, our safety contacts MG and Kib for agreeing to raise the alarm should we fail to show, and finally a hat tip to all those whose dangerous and no doubt tiring work has made the trip continually possible in such an entertaining fashion.
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Further reading...

Croesor Rhosydd
UK Blitz - Croesor Rhosydd SC

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