Cwmorthin Slate Quarry Access Information

Photograph of Cwmorthin Slate Quarry

About Cwmorthin Slate Quarry

Cwmorthin Slate Quarry is a substantial disused slate mine found on the shores of Llyn Cwmorthin above the town of Blaenau Ffestiniog, North Wales. It is one of a number of slate mines that circle the town, most of which were enormous enterprises in their day. It has a long and complex history beginning in the early 1800's, with heavy underground development starting around 1860.

It was run by several different companies as a venture in its own right during the late 1800's. The earlier underground workings started at "Lake Level", so called due to the entrance being just above the surface of the nearby Llyn Cwmorthin, and ascended upwards in the mountain ultimately for 8 floors in both the Old and Back Vein. Poor working practices and reckless engineering decisions ultimately led to a substantial collapse and the end of that company.

A new company took the mine on afterwards and reused Lake Level but sealed off the shattered and dangerous upper floors. Instead, they developed new workings below, going down into the mountain. Ultimately this company sunk five floors on both veins, before itself being being forcibly closed in 1901 due to a legal dispute.

The now abandoned lower floors flooded up to Lake Level, containing an immense amount of water hundreds of feet deep, which remained until the early 1930's. The neighbouring mine (Oakeley Quarries) were at this time driving underneath the old Cwmorthin workings and were uneasy about having such a huge volume of water above them, so decided to drain it out. Special diamond-drilled bore holes were driven through into the deepest parts of Cwmorthin from Oakeley and the water drained out under controlled conditions.

When the water level reached the bottom, the mines were connected in several places by full-size tunnels and Oakeley (who'd taken over the ownership of Cwmorthin) actually re-opened some of Cwmorthin and put men to work in it. The Back Vein Incline was re-equipped and even a new incline was driven down another 90 vertical feet to open some more chambers.

Cwmorthin then operated essentially as just another part of Oakeley right up until 1970 when Oakeley itself closed. This marked the end of the mine's working life as a major concern, however, throughout the 1980's and early 1990's the mine was working on a limited scale by a small team of local men. Extraction occurred in a few chambers on Lake Level and Level 2.

The mine is presently leased as a caving venue by Go Below Underground Adventures but access is freely extended to other interested individuals and parties.

Access for Recreational Cavers and Mine Explorers

Permission is given to bona fide cavers and mine explorers to enter and explore the underground workings, at their own risk.

A key to the main adit is available free of charge (subject to a 20 deposit) from the Go Below Office in Betws-y-coed. The office is open 9am - 5:00pm every day.

Access for Professional Group Use

Cwmorthin Slate Quarry has a "Blue Route" through the workings approved for use with Outdoor Education Centres delivering residential courses. Commercial adult or family tourist groups require written consent from WMAG before the mine may be accessed for this purpose.

Most of the Blue Route requires Mine Leader Level 2 (or CIC). The group leader(s) must hold a current LCMLA or CIC ticket and valid adventure activity insurance that covers caving/mine-exploration.

A key to the main adit is available free of charge (subject to a 20 deposit) from the Go Below Office in Betws-y-coed. The office is open 9am - 5:00pm every day.

Important Information for All Users

The mine is gated at both adits in accordance with the land owners wishes. A key to the main adit is available free of charge (subject to a 20 deposit) from the Go Below Office in Betws-y-coed. The office is open 9am - 5:00pm every day.

Please approach the mine from the Cwm Orthin side taking note of any footpath diversions. Please show due respect for livestock, signage and fencing, and follow the country code. Digging, placing bolts/aids, collecting mineral samples or moving artefacts are all prohibited without prior consent from WMAG. The marking of the walls, leaving rubbish, or taking anything from the site is strictly forbidden.

It is also strictly forbidden to enter the former Oakeley workings beyond the "Boundary" marks. The mineral rights beyond this point are owned by Welsh Slate Ltd and trespassing into these areas could seriously jeopardise access to Cwmorthin for recreational explorers.

Access the Friends of Cwmorthin Website

The old website and forum for Cwmorthin is still online and available to interested parties, but due to technical difficulties with the old domain name, the address has had to move. You can find it at

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