Overview
The blue reservoir near the top of Turlough Hill isn’t natural, and neither is the name. At 681 m (2,234 ft) in the heart of the Wicklow Mountains, this is the site of Ireland’s only pumped-storage hydroelectric station – a piece of 1960s engineering that quietly helps balance the national grid while staying mostly out of sight beneath the mountain’s own cover. Two things define the hill: the wind-scoured granite ridge under blanket bog, and the sleek geometric reservoir perched near the summit.
For walkers, the reward is the height and the view. On a clear day it runs from the Irish Sea to the neighbouring summits of Camaderry and Conavalla, with the glacial corrie lake of Lough Nahanagan sitting in the valley below.
The name and history
Before the engineers arrived, the hill was known as Tomaneena, from the Irish Tuaim an Aonaigh, ‘mound of the assembly’. The name Turlough Hill came in the 1960s, when an ESB engineer named O’Riordan called it after his son Turlough during the site surveys; the echo of the Irish turlach, a seasonal limestone lake, is pure coincidence.
When the ESB planned the scheme in the mid-1960s, keeping the view at the Wicklow Gap unspoiled was a stated priority. It brought in landscape architect Sylvia Crowe, who advised planting the upper reservoir’s embankments and shaping the lower works to settle into the rock. To protect the skyline further, the transmission lines were buried for about a mile (1.6 km) out from the site before rising onto pylons down the King’s River valley – a choice that added some £600,000 to the cost but kept the mountain looking much as it always had.
The power station beneath the mountain
Construction began in 1968 and finished in 1974, the largest civil engineering job Ireland had taken on at the time. The principle is simple. When demand is low and power is cheap, surplus electricity pumps water from the natural Lough Nahanagan up to the artificial reservoir on the ridge; when demand spikes, the water is let fall back through pressure tunnels, spinning four reversible pump-turbines in a cavern measuring 76 × 21 × 27 metres inside the granite.
Four units of 73 MW give a combined 292 MW, and the plant can go from standstill to full output in 70 seconds – which is the whole point of it, catching sudden gaps in supply. A full upper reservoir holds about 1.59 GWh, enough to run at maximum load for more than five hours. The scheme cost IEP £22 million to build, and since 2004 it has doubled as the Hydro Control Centre for the ESB’s entire hydroelectric fleet. In 2024 the station marked its 50th anniversary.
Can you tour it?
Worth knowing before you build a day around it: you can’t just book a visit. The ESB doesn’t run regular public tours of the power station. It opens the doors only for occasional free guided tours – for the 40th anniversary in 2014, the 50th in 2024 and again in 2025, usually around National Heritage Week – and those places book out fast. If one comes up and you get on it, the tour goes inside the works. If not, the mountain itself can be walked any day of the year, though the reservoir at the top sits inside a fenced ESB compound: you can’t reach the water, and you can’t see the famous blue lake from the fence either. That view is an aerial one. The reward on foot is the summit panorama.
Walking Turlough Hill
The walking splits into a short option and a long one.
The short option follows the service road up from the Wicklow Gap, leaving it just below the fenced compound for a rough track to the true summit of Tomaneena (682 m) – allow two to two and a half hours out and back. The bigger day is the Camaderry circuit from the same car park: roughly 12 km, heading past Lough Nahanagan and over Camaderry (698 m) on the ridge between the Wicklow Gap and Glendalough. Allow five hours or more. The upper reaches open into bog with sweeping views once you’re up. Across the road on the north side of the gap, Tonelagee (817 m) is a separate mountain and a separate walk, about 4.5 km out and back.
What to look out for on the trail:
- Glacial features: Lough Nahanagan is a textbook corrie lake, gouged out by ice in the last glaciation and now the scheme’s lower reservoir.
- Alpine flora: For its modest height, the exposed ridge grows plants you’d expect much further north – dwarf willow, cowberry, crowberry, fir clubmoss and common bilberry, among heather, purple moor-grass and Sphagnum moss.
- Trail conditions: Well used but soft and uneven across the bog. Sturdy boots with ankle support, especially after rain.
- Near the summit: an old quarry edge close to the top has a fence in poor repair – keep children and dogs close, especially in mist.
Practical information
- Parking: Free at the Wicklow Gap car park and at the Turlough Hill car park nearby. The tarmac road from the gap to the summit area is the ESB’s private service road, behind a barrier: walkers and cyclists have long used it and it is the usual way up, but it isn’t a public right of way, so treat access as a courtesy rather than an entitlement and follow any signage.
- Best time to visit: Spring through autumn for the steadiest weather and the best of the moorland colour. The summit is exposed to wind and sudden cloud year-round, so check the forecast and pack waterproofs and layers.
- Preparation: Carry a map or GPX file, bring water and food, and follow Leave No Trace. Mobile signal is patchy, so tell someone your route and return time.
- Nearby stops: The Glendalough monastic site and lakes are a short drive down the valley to the east, and the village of Avoca has pubs and cafés for afterwards. St Kevin’s Way, the old pilgrim path to Glendalough, crosses the Wicklow Gap itself.
Don’t plan the trip around a station tour – they’re rare and fill in minutes. Come for the walk instead, and start early for the quietest parking and the best chance of a clear summit.