About
Electric Mountain is one of Britain's most extraordinary and unusual visitor experiences — a guided journey deep inside Elidir Mountain above the village of Llanberis in Snowdonia to see the Dinorwig Pumped Storage Power Station, the largest underground power station in Europe and one of the greatest engineering achievements of the 20th century.
The power station was constructed between 1974 and 1984, requiring the excavation of over a million tonnes of slate rock from the interior of Elidir Mountain to create a vast network of caverns, tunnels and waterways. At the heart of the complex is the machine hall — a cathedral-like underground chamber measuring 180 metres long, 24 metres wide and 60 metres high, larger than the interior of St Paul's Cathedral in London. Six reversible pump-turbine units, each weighing 450 tonnes, are housed in this cavern. Above the mountain, the upper reservoir Marchlyn Mawr can hold 7 million cubic metres of water; below, Llyn Peris provides the lower reservoir.
The principle of operation is elegant: during periods of low electricity demand (typically at night), surplus electricity from the National Grid pumps water from Llyn Peris up through the mountain to Marchlyn Mawr. When demand peaks — during half-time of major football matches, after popular television programmes end, or during periods of cold weather — the water rushes back down through the tunnels, spinning the turbines to generate up to 1,728 megawatts of electricity within just 16 seconds. This makes Dinorwig Britain's emergency power reserve and one of the fastest-response electricity generation facilities in the world.
The free visitor centre at Llanberis explains the technology of pumped storage hydroelectricity through interactive displays, models and films. Guided bus-and-walking tours take visitors into the mountain itself, descending to the machine hall to see the giant turbines at close range and experience the scale of this underground industrial marvel. The setting in Snowdonia National Park, surrounded by the dramatic landscape that was itself shaped by the slate quarrying industry the mountain was once part of, adds an extraordinary context — the same mountain that produced roofing slate for Victorian Britain now stores electricity for modern Britain.
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Plan Your Visit
💡 Visitor Tips
- Book the underground tour in advance, especially during summer holidays and half-term — tours sell out on busy days.
- The temperature inside the mountain is constant at around 12°C regardless of outside weather — bring a warm layer even in summer.
- The visitor centre is free — if tour tickets are sold out, the free centre and café still offer a worthwhile visit.
- Wear comfortable, closed-toe shoes — the underground tour involves walking on industrial surfaces and some steps.
- The café has excellent views over Llyn Peris and the former Dinorwig slate quarry — worth lingering over lunch.
- Allow the full day to combine Electric Mountain with the adjacent National Slate Museum, Llanberis Lake Railway and Padarn Country Park.
- The Snowdon Sherpa bus network makes it easy to visit Llanberis without a car from Caernarfon, Bangor or other Snowdonia centres.
- Children fascinated by the underground tour should also visit the National Slate Museum next door — it shows what Elidir Mountain was like before it became a power station.
Highlights
Discover the unique exhibits and collections at this museum.
Collections
Power from the Mountain
The story of Dinorwig Pumped Storage Power Station — how it works, why it was built, and its role as Britain's emergency electricity reserve, explained through interactive displays and scale models.
Building Dinorwig: The Construction Story
The remarkable engineering and human story of constructing the largest pumped storage station in Europe inside a Welsh mountain between 1974 and 1984.
Energy for Tomorrow: Pumped Storage and Renewables
How pumped storage hydroelectricity is becoming increasingly important in a renewable energy future, balancing the intermittent supply of wind and solar power.
Current Exhibitions
No current exhibitions. Please check the museum website for updates.