Fascinating facts you didn’t know about the power station buried deep within a mountain

Inspired by Sir Edward MacColl in the 1930s, construction began in 1959 and took six​ years to complete.

Cruachan Power Station was officially opened by Queen Elizabeth II on 15 October 1965.​ It’s been generating power for 60 years, delivering electricity to hundreds of thousands of​ homes and businesses.

The turbine hall with its four generators is located 1km within the hollowed-out mountain of​ Ben Cruachan, which rises to 1,126 metres (3,694ft) and is the highest in Argyll and Bute.

The access tunnel, cavern and the networks of passageways and chambers were blasted​ and drilled by a workforce of around 1,500 men, known as the Tunnel Tigers, in the late​ 1950s to early 1960s. They came from all over Scotland, Ireland and Europe, working in​ different roles as engineers, joiners, builders, on the dam and blasting tunnels. Fifteen people died while digging and blasting the power station’s tunnels and constructing the dam.

The Tunnel Tigers set an unbroken world record for hard rock tunnelling, driving 560ft in​ seven days in 1965.

Power to the people: 60 years of Cruachan, Scotland’s hollow mountain and an engineering marvel

The film Andor: A Star Wars Story, and prequel, which was released in 2022 was filmed in​ the tunnels and around the dam at Cruachan, with local actors and assistants involved.

Bought by Drax in December 2018, the site is one of only four pumped storage hydro stations in the UK and the largest in Scotland.

Cruachan Power Station’s Hollow Mountain Visitor Centre has been awarded a Tripadvisor Traveller’s Choice award for 2025 due to top reviews, with more than 60,000 visitors each year. When the current refurbishment of the power station is complete the Hollow Mountain tours inside the mountain will resume.

On the walls of the turbine hall, 1km below the ‘hollow mountain’, you can find something unusual for a power station. There is a massive wood and gold leaf mural, measuring 14.6m long by 3.6m tall, featuring Celtic crosses and gold orbs that resemble the urban lights Cruachan helps power. It was created by artist Elizabeth Falconer to celebrate the power station’s opening by Queen Elizabeth II and there is a mini version in the Visitor Centre.

Ben Cruachan has a mythical guardian, Cailleach Bheur or “Old Hag of The Ridges", who protects a mountain top spring. She was tasked with covering its well with a slab of stone at sundown and lifting it away at sunrise but fell asleep, causing the well to overflow and creating Loch Awe. The story is told in the mural.

Pumped storage hydro is one of the oldest forms of large-scale energy storage requiring two reservoirs based at different altitudes but close to each other. Sitting on Loch Awe, Cruachan fits the bill perfectly thanks to the diorite and phyllite rock, a softer type of granite, and the abundance of water.

It works like a giant water battery. When power is plentiful, water is pumped from the lower to the upper reservoir using reversible turbines and stored behind Cruachan’s huge dam wall. Then, at times of high demand or when the grid needs more energy to fill gaps from weather dependent renewables, like wind or solar, the water is released downhill into the lower reservoir, driving the turbines the other direction to generate electricity.

The power station has a capacity of 440 megawatts (MW) – enough to power hundreds of thousands of homes – and can react to dips in power within seconds. It takes less than 30 seconds to reach full generating capacity.

The reservoir has a storage capacity of 10 million m³ of water and a catchment area of 23km². That’s equivalent to 4,000 Olympic swimming pools.

Coinciding with its 60th anniversary, Cruachan is undergoing a major £80m refurbishment. Its generating units – the machinery which creates electricity as water rushes through its turbines – were commissioned in 1965 and contain parts, including their turbines, which are now 60 years old.

The project will see the power station’s generation capacity increased by 10% to 480MW helping it to power thousands more homes.

The huge valves which control the waterflow through the power station’s turbines will be replaced. Each valve weighs as much as three double decker buses, and in one minute can allow through water to fill an Olympic swimming pool.

A new transformer will also be installed, transferring electricity from the station to the grid and, from there, into TVs, kettles, offices and factories.

The upgrade project will take three years to complete. During the upgrade the number of jobs supported by the power station will triple, helping to bring new opportunities and skills for years to come.

More than 10% of the power station’s workforce are local apprentices.

The designer of Cruachan, James Williamson, a civil engineer from Lanarkshire, spent his weekends taking his children walking in Scotland’s hills to see if they would be suitable for hydro power stations.

​The people behind Cruachan Power Station talk about their work and pride in the engineering marvel, which has been supplying power to Scotland for 60 years and counting

When Queen Elizabeth II opened the power station in 1965 a special platform was constructed on scaffolding in the turbine hall to support the seated VIPs. Below this the Tunnel Tigers snuck in to witness the opening of the building and when the VIPS sat down, coins fell out of their pockets and showered down on them.

In one of the tunnels inside ‘The Hollow Mountain’ is ‘the fairy grotto’, the only area in the power station ever painted white, because it is said The Queen walked this corridor and a carpet was also laid. In this section there are fairy dolls, including Tinker Bell, and sketches and notes on the wall left by workers.

Cruachan frequently completes biodiversity surveys to monitor the species living in the surrounding habitats. This helps to build a picture of the mammals, birds and insects present, which includes a number of protected status species and those of highest conservation concern such as the great black-backed gull.

Birds recorded also include osprey, Canada geese, woodpecker, northern wheatear, common cuckoos, whinchat, mistle thrush, wood warbler and tree pipit. House sparrow and common mallard have nested successfully at the station recently for the first time.

Six species of mammal were recorded in 2024, including the European otter and bank vole, and pine martens and red squirrels have been spotted near the Visitor Centre cafe.

A total of 157 species of invertebrates were recorded including dragonflies, grasshoppers, true-bugs, beetles, moths and butterflies.

In 2024, 217 moth species were found at the station, including five new species listed as “nationally scarce”.

13 species of bee and wasp were recorded, including a new species of sawfly and the ‘nationally rare’ mining bee and in 2023 the rare Scottish cranefly was recorded at the Visitor Centre – the first sighting for Argyllshire.

As part of the 60th anniversary celebrations, Cruachan is inviting everyone to share memories of the power station through photos and videos from years gone by to [email protected]