Overview
Lough Ouler is the heart-shaped lake you’ve seen on Instagram, but the heart only appears from above. Down at the shore it’s just a mountain lake in a steep corrie; climb the slopes of Tonelagee and the water and the ground around it resolve into a near-perfect heart. That’s the catch worth knowing before you set out: the reward is at the top, not the lakeside, and getting there is an unmarked, boggy climb in Wicklow Mountains National Park. There’s no entry fee. The corrie was scooped out by a glacier during the last Ice Age, and Tonelagee above it stands 817 m – the third-highest peak in the Wicklow Mountains and the 33rd-highest in Ireland.
The routes
Two approaches cover most visits. Neither is waymarked, and both share the same rough, wet character.
- Wicklow Gap (R756) – The usual way up. From the Wicklow Mountains Viewing Platform car park (also called the Turlough Hill car park), it’s roughly 9 km return with about 500 m of ascent, 3.5–4 hours, either over the Tonelagee summit or contouring to the lake.
- Glenmacnass (R115) – From the Glenmacnass Waterfall car park, an 8 km loop with around 450 m of ascent, 3–4 hours. The track climbs steeply through a river valley and passes a standing stone between Stoney Top and Tonelagee.
Carry a 1:25,000 Ordnance Survey map and a reliable GPS app with offline maps downloaded – mobile signal is patchy across the ridge. Share your route and expected return time with someone before setting off. River crossings on the Glenmacnass approach can turn hazardous after heavy rain, so check water levels and be ready to turn back.
Seasonal conditions and safety
Weather in the corrie changes quickly, and the ground underfoot decides how hard the day is.
- Spring and summer (April–October) – The reliable window. Longer days, and the ground firms up after dry spells. Heather blooms from mid-summer.
- Autumn – Lighter foot traffic and golden slopes, but daylight shortens fast and rain is frequent.
- Winter – Snow and ice are common, the corrie holds deep drifts, and frozen bog turns treacherous. Only attempt it with cold-weather mountaineering experience and the right gear.
Waterproof boots are non-negotiable. Gaiters help over wet tussock, and poles steady you on the steep, uneven ground. If mist drops visibility to a few metres, navigate carefully or retreat to ground you can read.
Can you swim in Lough Ouler?
Yes, entirely at your own risk. Nothing prohibits it, but this is cold, open mountain water in a corrie with no safety cover of any kind, no marked zone and nobody within earshot. Power-boating, water-skiing and jet-skiing aren’t permitted. Anyone getting in should be experienced in cold water, never alone, and carrying dry layers for the walk back out. See swimming in Ireland’s lakes for how Wicklow’s lakes compare, including the ones with no legal access at all.
What to see
The draw is the view from above. Climb to Tonelagee or the nearby Stoney Top and the Wicklow valleys open out around you; on a clear day the Irish Sea glints to the south-east, with Mullaghcleevaun and Lugnaquilla framing the horizon. The heart shape reads best from these high points, which is why the summit is worth the extra push over stopping at the shore.
Wildlife keeps its distance. Red deer browse the heather at dawn and dusk, meadow pipits and curlews work the slopes, and birds of prey patrol overhead. Look closely and the corrie holds rare arctic-alpine plants – mossy saxifrage and alpine lady’s-mantle among them. The area is also a favourite with trail runners, and the Wicklow Glacial Lakes race routes through the corrie.
Parking and access
Both trailheads use free, unmanaged car parks that fill quickly on sunny weekends.
- Glenmacnass Waterfall car park – Off the Old Military Road (R115). Arrive early; space is limited.
- Wicklow Mountains Viewing Platform car park – Near the Turlough Hill point on the R756. Larger, but still busy in peak season.
- From Glendalough – The trailheads are about 20 minutes’ drive from the Glendalough monastic site, so a morning here pairs well with an afternoon in the valley.
- Public transport – Bus 181 (St Kevin’s) runs from Dublin to Glendalough. From there you’ll need a local taxi to reach the car parks, so book ahead.
Practical tips
- Gear checklist: Waterproof boots, gaiters, map/GPS, head torch, warm layers, high-energy snacks and at least 1.5 litres of water. There are no facilities at any trailhead.
- Dogs: Welcome on lead. The terrain is rough on paws, and livestock may graze the lower slopes.
- Photography: Golden-hour light hits the corrie from the west in late afternoon. Sunrise means a pre-dawn start and a good headlamp.
- Leave no trace: The bog is fragile. Stick to established tracks, take all waste home, and avoid trampling heather.
Check the mountain forecast before heading up and allow extra time for navigation. And remember the whole point is the aerial view: from the lakeshore it’s just a lake, so save some legs for the climb to Tonelagee or Stoney Top.