Overview
The two lakes at the bottom of Glenasmole aren’t natural. They are Victorian reservoirs, built between 1883 and 1887, and they still send around 18.2 million litres of drinking water a day to some 35,000 South Dublin homes. Fifteen kilometres southwest of the city, the valley sits between the Dublin Mountains and the edge of Wicklow National Park, and for all that municipal work it stays a quiet, workaday escape for walkers, birdwatchers and families. If you have ninety minutes, walk the short Lower Reservoir Loop; the only real catch is the parking, not the walking.
History and mythology
The valley itself dates to the last Ice Age, when retreating glaciers carved its U-shape. The name carries two possible meanings: Gleann na Smól(aigh), ‘valley of the thrush’, or Gleann na Smóil, ‘valley of the burnt patch’, a nod to the legendary burning of the Dá Derga hostel in early Irish myth. Nearby Bohernabreena comes from Bóthar na Bruíne, ‘the road to the mansion’, tying the place to old tales of hospitality and chieftains.
The area is woven into the lore of Fionn Mac Cumhaill and Na Fianna. Local tradition holds that Fionn hunted red deer and the now-extinct great Irish elk through these woods, feasting afterwards on the summit of Seefin, whose name means ‘the seat of Finn’. Another legend puts the poet-warrior Oisín here: returning from Tír na nÓg, he leant from his white horse to help locals lift a boulder, touched Irish soil, and aged 300 years in an instant.
The reservoirs are the tangible history. The Bohernabreena Waterworks were built in the 1880s to tame the flood-prone River Dodder, power the mills downstream and supply clean water to Rathmines. The system still runs to its original logic: the upper lake collects the clearer, non-peaty water for drinking, the lower holds the peaty runoff that once served the mills, and a stone-lined channel links the two before the water reaches the treatment works at Ballyboden. Near the lower loop stand the ruins of St Anne’s Graveyard, its church in use until the mid-16th century. Closed to burials because of its closeness to the water supply, the site still hosts an annual Mass each July and keeps a ‘Strangers’ Corner’ for those buried away from home.
What to see and do
The reservoir walks
Two loops suit different time budgets, both starting from car parks.
Lower Reservoir Loop (short) About 4 km and 1 to 1.5 hours, this is the one most people come for. It starts near the new Upper-Lake car park; head clockwise from the trail entrance so you take in the water’s edge and mixed woodland before reaching the ruins of St Anne’s Graveyard, then loop back.
Upper Reservoir Loop (long) The 8.5 km loop takes roughly 60 to 90 minutes at a steady pace. Starting from the original Bohernabreena car park, it opens with a stretch of quiet country road – no footpath on that first section – then drops to the lower reservoir, climbs gently to the upper lake and follows the historic stone channel home. The rest is well-trodden and manageable for most.
Dublin Mountains Way – Stage 8
For distance, join Stage 8 of the 42.6 km Dublin Mountains Way. This 6 km segment runs from Glenasmole to Tallaght, following the River Dodder through Kiltipper Park and past residential greenways. Look for the national yellow hiker symbol and the directional arrows.
Two newer stops
Two smaller ventures have set up in the valley: Sophie’s Sauna, a hot-and-cold sauna by the water, and Ollie’s Honey Farm, which runs beekeeping tours and honey tastings. Both are worth checking ahead for opening times before you build a day around them.
Flora and fauna
The valley’s damp, peat-rich soils and open water make it a Special Area of Conservation. Spring brings wild orchids, including early purple and frog orchids, across extensive molinia meadows, and the petrifying springs leave mineral crusts where the calcium-rich water evaporates.
The birdlife is the reliable draw. Along the water you’ll see herons, moorhens, grey wagtails and dippers, with the odd kingfisher; meadow pipits and skylarks work the open grassland, and winter brings waders such as curlew and snipe. Anglers should note that trout fishing is by permit only, from a local angling club, and by fly rod.
Practical information
Parking and access
The valley is open around the clock and free to enter, but parking is the thing to plan. The original car park at the north end has just 15 free spaces and fills fast at weekends, and roadside parking is enforced – cars are regularly towed. The surer bet is the newer Upper-Lake car park, which charges €5, is secure and has toilets; a coffee stall, Goughie’s, sets up there at weekends.
Public transport
On Saturdays the Local Link Kildare South Dublin Route SD03 stops at the Upper Reservoir Gate and the Glenasmole Community Centre. Check the TFI Live app for real times, as rural services can be thin.
Amenities and accessibility
Toilets are at the Upper-Lake car park. The Glenasmole Community Centre, about 9 km from Tallaght, has tea and coffee and is open Monday to Friday 9am–9pm and weekends 9am–5pm, closed on bank holidays. Dogs are welcome on all trails but must be kept on a lead throughout, for the ground-nesting birds and the livestock. The paved path from the Upper-Lake car park to the reservoir edge is flat; the loop trails themselves are uneven and boggy in places.
Visitor tips
- Arrive before 10am at weekends for parking and quiet.
- Wear waterproof boots; the trails turn muddy after rain.
- Mobile signal is patchy in the valley, so download offline maps.
Nearby highlights
- Cruagh Wood (20-minute drive) – the Slí na Sláinte loop, with views over Dublin from 522 m.
- Blessington (25-minute drive) – a lakeside town with the Blessington Greenway and Russborough House close by.
- Ticknock (30-minute drive) – the Fairy Castle passage tomb and views over Dublin Bay.
Late spring catches the orchids; autumn turns the deciduous woods and sets them reflecting in the reservoirs. On the short loop, take the second entrance at the trailhead and keep clockwise, so you reach St Anne’s Graveyard before the car park.