Electric Mountain is the visitor centre for Dinorwig Power Station, a pumped-storage hydroelectric facility built inside the old Dinorwig quarry between 1974 and 1984. The scale is extraordinary: 16 kilometres of underground tunnels were excavated through the mountain, with a main cavern large enough to contain St Paul's Cathedral. The station can go from zero to 1,800 megawatts of output in under 16 seconds, making it Britain's emergency electricity reserve.
Guided tours take visitors inside the mountain on a bus, through the tunnels to the turbine hall and the machinery rooms. The tours run regularly in summer and must be booked in advance. The visitor centre is free to enter; the underground tour carries a charge. It is one of those places where the engineering ambition is genuinely jaw-dropping.