Dorothea, an old slate quarry in Wales where 21 divers have already died

Abandoned places always have certain risks, but there are some that are especially dangerous, at least for certain activities.

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The Nantlle Valley in North Wales was a major slate-producing area, with as many as 37 quarries excavated in the 19th and 20th centuries. The largest of these was Dorothea Quarry near Talysarn in Carnarvonshire (Gwynedd in Welsh). This quarry was opened in the 1820s, eventually employing 350 men and producing 5,000–6,000 tonnes of slate per year, with a peak output of over 17,000 tonnes in 1872.

Dorothea's production declined in the second half of the 20th century. Finally, the quarry was abandoned in 1970, and a large part of it was flooded, creating three lakes. The rest became majestic slate ruins that resemble an ancient castle from ancient times. At the bottom of the quarry, underwater, old quarry buildings and some machinery that had been used there remained. In addition, cars were piled up in the western area in the following decades.

As a result, Dorothea became a magnet for scuba divers, with fatal consequences: between 1994 and 2004, 21 divers died there from various causes. One of them is that the quarry is almost 100 meters deep and some divers were not prepared to dive so deep. Added to this are the numerous traps posed by the accumulation of abandoned remains at the bottom. For a few years now, Dorothea has been reserved for experienced, well-equipped divers to prevent further deaths. Two years ago, Mike Smith SCUBA & Technical Diving UK published a video of a dive at Dorothea using special equipment and up to a depth limit of 60 meters:

This Sunday, Stephen J. Reid published one of his always entertaining exploration videos showing the surface of Dorothea and explaining which parts are especially dangerous and which ones are safe to walk on, with certain precautions:

You can see some screenshots from Stephen J. Reid's video here. The ancient ruins, overshadowed by vegetation, look like an ideal setting for a fantasy film.

The owners of Dorothea used the slate from the quarry to build their buildings. Some have now become ruins that appear much older than they actually are.

The most beautiful building in Dorothea is the former Talysarn Hall Chapel, a Gothic-looking church that provided religious assistance to the miners. It is the oldest building in the quarry, dating back to the 18th century, before slate mining began there. According to Keithwhiddon.uk, in 1905 the chapel was converted into a quarry office building, and later became the estate gardener's house. It is now derelict.

One of the most dangerous parts of these old ruins is the Nantlle Tramway Tunnel. According to Coflein.gov.uk, this tramway was built between 1825 and 1828. The tunnel, made of slate blocks, was abandoned in 1889. As you can see in the video, some sections are collapsing.

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Images: Stephen J. Reid.