Cwmorthin Slate Mine will host the deepest rave ever attempted on Thursday 15 October 2026, and you almost certainly cannot go. Roni Size plays 1,375 feet below the mountains of Eryri, the ballot to get in closes on Friday 9 October, and only a limited number of winners will make the descent.
That is the version running on every music site this week. Most of it skips the mine. Cwmorthin has been worked since 1810, once employed more than 500 men, and sits inside a World Heritage Site above Blaenau Ffestiniog.
This guide covers the event, the depth, the sound, the quarry, the walk you can do without a ballot place, and where to stay.
Quick Facts
Region: Eryri (Snowdonia), Gwynedd, North Wales
Best for: Industrial heritage, live music news, short quarry walks
Getting there: By road to Tanygrisiau, or by Ffestiniog Railway to Tanygrisiau halt
Time needed: Half a day for the quarry walk; the rave itself is by ballot only
Cwmorthin Slate Mine: 1,375 Feet Down
G-SHOCK, the Casio watch brand, is staging the rave with the underground operator Go Below to launch its GDG-B100 MUDMAN watch. Roni Size, the drum and bass producer behind the Mercury Prize-winning album New Forms (1997), plays the set.
Places go to public ballot winners through the G-SHOCK website. Entries close on 9 October. Winners must meet age, fitness, clothing, and equipment requirements, and they reach the chamber via miners’ stairways, waterlogged passages, underground ravines, scrambles, zip lines, and abseils.
The organisers will submit the night as a record attempt for the world’s deepest underground rave. That is subject to independent verification.
The watch is built for this kind of place. The GDG-B100 MUDMAN is shock-, dust-, and mud-resistant, with 20 bar water resistance, and it costs £200. The first attendees receive it before it reaches the shops.
Everyone else can listen. G-SHOCK Radio streams the set via Starlink on 15 October, and the full set follows on Mixcloud.
Where to Stay: Oakeley Arms is a family-run stone hotel at Tan y Bwlch, Maentwrog, with single, double, twin and family rooms, plus a restaurant and bar serving Welsh dishes.
Worth Knowing: One report calls the chamber the deepest point beneath the earth in the UK open to the public, according to the Herald.Wales. Treat that as the organisers’ claim until the record is verified.
The Hotel That Proved the Depth
The 1,375 feet is not new. Go Below opened a hotel called Deep Sleep in the same mine in April 2023, at the same depth. That is 419 metres.
A 2023 report in the Shropshire Star describes a descent of about an hour through old workings, over ancient miners’ stairways, decaying bridges and scrambles. Guests wear a helmet, a light, a harness, and Wellington boots.
The journey starts well before the mine. The 2023 report has guests meeting at a base in Tanygrisiau, then walking uphill for 45 minutes to a cottage to collect their kit. Add the hour underground, and you are well over an hour and a half from the car park to the cabins, before any music starts.
The cabins are small. Wikipedia lists four twin-bed cabins and one grotto with a double bed.
The same report says the operation is inspected by independent mine engineers through the Mines Inspectorate, and names Miles Moulding as Go Below’s founder.
Where to Stay: Deep Sleep, run by Go Below, offers underground cabins and a grotto cut from slate. Check current availability and prices with the operator, because the 2023 prices are out of date.
Worth Knowing: The grotto room sits in a cavern the miners carved out of the slate more than a century ago.
Turning a Mountain Into an Instrument
The sound design is the real story. A normal rave pushes sound out into a room. This one pushes it into the rock and listens for what returns. Vibration transducers will drive Roni Size’s set into the slate. Geophones and hydrophones will record frequencies travelling through rock, mud and water, and that response will feed back into the live mix, according to EDM.com.
Size calls it “the most underground of underground raves ever”. The sound goes into the mountain, moves through slate, rock and mud, and comes back changed.
Where to Stay: The Oakeley Arms bar stocks real ales, ciders, Welsh gins and whiskies, which suits the evening after a day on wet slate.
Worth Knowing: Size plays Bristol’s Lloyds Amphitheatre on 25 June 2027 for the 30th anniversary of New Forms, with Fabio and Grooverider supporting, according to MusicRadar.
1810 to the 1970s: The Quarry Under the Rave
The Casson family opened a small quarry at Cwmorthin, west of Tanygrisiau, in 1810. By 1882, it employed over 500 men and ran three mills.
The Cwmorthin Slate Company was formed in 1861. The Oakeley company took the quarry over in 1902. Wikipedia gives the official closure as 1970, with small-scale work through the 1980s and 1990s and a final closure in 1997. Go Below says mining continued sporadically until the 1970s.
Where to Stay: Deep Sleep puts you inside the workings themselves, in the same mine that employed those 500 men.
Worth Knowing: Sources disagree on the final end date. The official closure was 1970, and work was sporadic after that.
Walking to Cwmorthin Yourself
Park at the Cwmorthin car park (LL41 3ST). A 1.9 mile (3 km) route reaches the quarry and Llyn Cwmorthin, passing Cwmorthin Waterfall, according to GPS Routes. For a longer circuit, head on towards Foel Ddu, Rhosydd Quarry and Moel-yr-hydd. Mud and Routes calls the Rhosydd route a half-day walk or a trail run. A second guide from the Oakeley Arms lists a 4-mile moderate route from a car park near Ffestiniog Power Station.
Along the way, Cwmorthin Terrace once housed workers and families in 13 original homes dating from the early 1800s. Rhosydd Barracks held two rows of buildings for single miners, in conditions the guide calls overcrowded, cold and wet. Capel Rhosydd served as the miners’ only place of worship and as a school.
Plas Cwmorthin was built in 1860 by the Rhosydd Slate Company for its manager. Coflein records managers living there until the early 1930s.
Wet slate is dangerously slippery underfoot. The ruins are unstable, and you should never enter mine shafts without caving experience and the owner’s permission.
By train, the Ffestiniog Railway stops at Tanygrisiau, an unstaffed halt where trains call on request. The station is close to the Cwmorthin waterfalls, and the current station opened on 24 June 1978. The original station opened in March 1866 and closed to passengers in 1939. On the way up from Porthmadog, the train passes Tanygrisiau pumped-storage power station and Llyn Ystradau, so you see the working valley before the ruined one.
Where to Stay: The Oakeley Arms also offers holiday cottages, which suit a walking group.
Worth Knowing: The manager’s house had four ground-floor rooms and a cellar, a long way up the hill from the barracks.
The Slate Landscape Around It
Cwmorthin lies within the Slate Landscape of Northwest Wales, designated a World Heritage Site in 2021. It is the fourth in Wales, after the Pontcysyllte Aqueduct, the Blaenavon Industrial Landscape and Edward I’s castles and town walls in Gwynedd.
It has six component areas. The Ffestiniog Slate Mines, Quarries and railway to Porthmadog is one of them, according to Gwynedd Council.
If you cannot get a ballot place, there are other underground options. Visit Wales lists the Zip World Llechwedd Deep Mine Tour, a 500-foot descent on Britain’s steepest cable railway. It also lists Go Below’s Ultimate Xtreme, a seven-hour package that it says includes the world’s longest and steepest underground zip line and a 70-foot underground free fall. Go Below’s other main trip, Hero Xtreme, is aimed at people with moderate fitness. Neither suits anyone with severe claustrophobia or a fear of heights.
Zip World Llechwedd also runs Bounce Below, six trampoline-style nets across a cavern, the highest hanging 180 feet above the floor.
Where to Stay: The Oakeley Arms sits in the Ffestiniog valley, within reach of Blaenau Ffestiniog’s underground attractions.
Worth Knowing: The Llechwedd tour goes down 500 feet. The rave goes down 1,375.
Practical Tips
- The ballot closes on Friday 9 October on the G-SHOCK website. Read the age, fitness and equipment requirements before you enter.
- Listen live on G-SHOCK Radio on 15 October. The full set follows on Mixcloud.
- Park at Cwmorthin car park, LL41 3ST, for the short quarry walk.
- Wear boots with grip. Wet slate is dangerously slippery.
- Stay out of shafts and ruined buildings.
- Trains call at Tanygrisiau halt on request, so signal the driver.
Responsible Visiting
Keep to the paths and out of the workings. Go underground only with an operator such as Go Below. Take your litter home and leave the ruins as you found them: they are unstable and were people’s homes.
Reader Q&A
When is the world’s deepest rave?
Thursday 15 October 2026, at Cwmorthin slate mine near Blaenau Ffestiniog in Eryri, 1,375 feet (about 419 metres) below ground.
Can I buy a ticket?
No. Places go to ballot winners. Entries close on the G-SHOCK website on 9 October.
Can I hear it if I do not win a place?
Yes. G-SHOCK Radio streams it via Starlink on the night, and the full set goes to Mixcloud afterwards.
Who is organising the rave?
G-SHOCK, the Casio watch brand, with Go Below, the underground adventure operator that manages the Cwmorthin mine. Go Below also provides the guides who lead the route down.
What do I need to take part?
The ballot terms set requirements for age, fitness, clothing, and equipment. Read them before you enter. Go Below’s own trips ask for moderate fitness and suit neither severe claustrophobia nor a fear of heights.
Can I visit Cwmorthin without a ballot place?
Yes, on the surface. There is a short walk from the car park to the quarry and lake. Underground trips need a guided operator.
Where to Stay
Oakeley Arms, Maentwrog. A family-run stone hotel at Tan y Bwlch with single, double, twin and family rooms, a restaurant and bar, and holiday cottages.
Deep Sleep, Go Below, Blaenau Ffestiniog. Underground cabins and a slate grotto at 1,375 feet. Check current availability and prices with the operator.
Closing
On the night of 15 October, the valley above Tanygrisiau will look as it does every autumn: wet slate, a mountain lake, a ruined barracks on the hill. Underneath, a set will go into the mountain and come back changed. The stream will still be running past the Cwmorthin waterfall in the morning.
For more Welsh autumn events, read Calan Gaeaf at Chirk Castle and St Fagans Ghost Tours 2026.
