At a glance
Europe's largest pumped-storage power station, carved inside the mountain above Llanberis — visitor centre free; underground tour into the colossal machine hall cavern from £15 (pre-book at electricmountain.co.uk). Adjacent to Snowdon Mountain Railway and Llyn Padarn. LL55 4UR.
About Electric Mountain — Dinorwig Power Station
Electric Mountain is the visitor name for the Dinorwig (Dinorwic) Pumped-Storage Power Station — an extraordinary feat of civil engineering hidden almost entirely inside the Elidir Fawr mountain above Llanberis. Construction began in 1974 and took 10 years: 10 million tonnes of rock were excavated to create a network of tunnels, caverns and chambers inside the mountain, with the main machine hall — 180 metres long, 23 metres wide and 60 metres high — being one of the largest underground chambers in Europe.
The power station operates by pumping water from Llyn Peris at the valley floor up to the Marchlyn Mawr reservoir (hidden behind the mountain ridge) during periods of low electricity demand, then releasing the water back down through the turbines to generate electricity when demand is high. The six turbines can be brought to full power in under 12 seconds — making Dinorwig one of the fastest large generators in the national grid, used to respond instantly to sudden spikes in demand such as the surge that occurs at half-time in major televised sports events.
The Electric Mountain visitor centre on the shore of Llyn Peris in Llanberis provides free access to exhibitions about the power station's construction and operation. Guided underground tours — by bus through the access tunnel and by lift into the machine hall — must be pre-booked and are subject to operational availability. The tour is a genuinely awe-inspiring experience: the scale of the underground caverns, carved from solid rock and housing machinery the size of houses, is unlike anything else in North Wales.
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Frequently asked questions
Dinorwig (Dinorwic) is a pumped-storage hydroelectric power station constructed inside the Elidir Fawr mountain above Llanberis between 1974 and 1984. It is Europe's largest pumped-storage facility, with an output of 1,728 megawatts. The station works by pumping water from Llyn Peris (below Llanberis) to the Marchlyn Mawr reservoir (above the mountain) during periods of low electricity demand, then releasing the water back through turbines to generate electricity in under 12 seconds when demand spikes — making it one of the fastest large power stations in the world to respond to demand.
The guided tour takes visitors by bus through a 1.6-kilometre tunnel into the mountain and then by lift into the main machine hall — a cavern 180 metres long and 60 metres high, housing six turbines and generators. The scale of the underground construction is extraordinary: the machine hall alone is the equivalent of a 16-storey building. The tour explains how pumped-storage works and includes a view of the operating turbine hall from a gallery above.
Tours operate year-round subject to the power station's operational schedule — on days when the turbines are running at full capacity, tours may be delayed or cancelled for safety reasons. It is worth noting that a visit on an active day — when the turbines are generating — gives a more impressive experience, with the sound and vibration of the machines audible in the machine hall.
Yes — the visitor centre at the lakeside in Llanberis is free to enter and has exhibitions explaining the power station's construction and operation, interactive displays and a café. Only the underground tour (from £15 adult) is charged. The visitor centre can be combined with a walk around Llyn Padarn or a visit to the National Slate Museum (also free) for a full morning without significant cost.
The construction of Dinorwig Power Station was one of the largest civil engineering projects in British history. Over 10 million tonnes of rock were excavated from inside the mountain, and the construction employed 2,500 workers for 10 years. The project was designed to have minimal visual impact on the Snowdonia National Park — all the machinery is hidden underground, and Llyn Peris (the lower reservoir) follows the valley of the original lake. The transformation of the site into a visitor attraction after completion was also a pioneering project in industrial tourism.
Tours must be pre-booked online at electricmountain.co.uk. Walk-up tours are not generally available. Tours operate on specific days and times, and availability can be limited — particularly in summer. The visitor centre is open on a broader schedule than the tours, so it is possible to visit the exhibition without having pre-booked a tour.