Croesor Quarry is a large underground slate mine in north Wales which was served by Croesor Tramway. Small scale quarrying began in the 1840s, and by 1861, there were two companies in operation. They amalgamated in 1865, a year after the quarry was connected to the newly opened Croesor Tramway. Much money was invested in development work, but volumes of useful slate produced were small, amounting to just 226 tons in 1868. Access to the underground workings was by a single adit, and the surface mill was powered by two water wheels. A change of ownership in 1875 did little to improve the profitability of the quarry, and it closed in 1878 or 1882.
Croesor Quarry is connected to the nearby Rhosydd Quarry by a tunnel that was built to aid surveying and settle boundary disputes. Apart from Chamber 1 East, a huge chamber in which the roof has collapsed, most of the accessible mine is in reasonable condition. Below the adit level, the mine is flooded and inaccessible. In spite of a series of collapses, particularly in the Rhosydd Quarry, an underground journey from Croesor to Rhosydd is still possible and is considered to be a classic trip for mine explorers. It is known as the Croesor–Rhosydd Through Trip. Fixed ropes, home-made suspension bridges, zip wires, and inflatable boats have been installed, which make it possible to complete the journey in comfort, although not necessarily in safety.
We wandered for a long time through landscapes that reminded us of Iceland, until we found our way down into the depths of the abandoned mines among the ruins of an old mining village. After a while, we had to tackle the first 30- and 40-meter descents by rappelling.
In some places the mines are flooded, and the beautiful blue water looks frightening in the gloomy, dark depths. A rope trolley is rigged above the lake, so we crossed the obstacle quickly.
The main thing is not to dangle, or you’ll get your ass wet in the cold water.
A suspension bridge over the lake.
The old miners’ ferries barely hold together. The massive logs have almost completely rotted.
Descending into the dark. At this point, you have to go down the rope straight into the boat in order to cross a particularly large underground lake.
The old suspension bridge collapsed many years ago.
Our team floating on an underground lake.
Going further, we found that the way to the exit was blocked. It took us a long time to climb over the latest rockfall and find a way out on one of the upper levels of the mine.
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Unfortunately, there aren’t many photos, but you can watch a video from these guys to get an idea of the route.