Overview
One of the highest caves in Ireland, Diarmuid and Gráinne’s Cave opens in the limestone face at the back of the Gleniff Horseshoe, high on the Annacuna cliffs in the Dartry Mountains, County Sligo. From the valley floor the dark archway is unmistakable, a massive natural opening with one of the widest mouths of any cave in the country, set into the sheer rock with the ground falling some 300 metres below it. The honest recommendation is to enjoy it from down there: the cave sits on private grazing land, and the owners would much rather people looked up at it than climbed to it.
The legend
The cave takes its fame from one of Ireland’s oldest stories, Tóruigheacht Dhiarmada agus Ghráinne (The Pursuit of Diarmuid and Gráinne). In the Fenian cycle, Gráinne, daughter of the High King Cormac Mac Airt, is promised to the ageing Fionn mac Cumhaill but falls instead for the young warrior Diarmuid Ua Duibhne. She drugs the wedding feast, the pair flee, and they spend their nights in a chain of hideouts the length of the country, the ‘beds of Diarmuid and Gráinne’. This cave is recorded as one of them: tradition has the lovers resting here before the final confrontation on Benbulben, where Diarmuid was gored by an enchanted boar. The tale survives in manuscripts going back to the 10th century, and dozens of caves, cairns and dolmens around Ireland still carry the couple’s name.
Geology and archaeology
The arch is cut from Carboniferous limestone laid down in a shallow tropical sea around 350 million years ago. The rock of the roof is studded with marine fossils and shells – a fittingly literal echo of Sligo’s Irish name, Slí Geach, ‘shelly place’. This is no show cave of dripping stalactites; it’s austere, scoured by glacial meltwater rather than built up by slow mineral deposits. Inside, a north-facing rift tunnel leads out to a balcony on the cliff, a tight ‘keyhole’ squeeze opens into a large southern chamber, and a lower series drops away by a ten-metre pitch. Excavations have turned up flint flakes, animal bones and a bronze hatchet set in stalagmite, evidence that people were using the cave in prehistory.
What to see and do
- View the arch from the valley: the limestone façade is dramatic against the sky and photographs well without any climbing at all.
- Spot wildlife: the surrounding crags and grassland support alpine plants like mountain avens and rock-rose, and peregrine falcons nest on the cliffs in spring and early summer, so bring binoculars.
- Walk the Gleniff Horseshoe loop: the cave overlooks this popular circular route through the glacial valley, with terrain from level valley tracks to higher ground.
- Photography: early or late light throws long shadows across the arch; a wide lens catches the scale, a telephoto the raptors.
Practical information and access
- Location: Annacuna cliffs, at the back of the Gleniff Horseshoe, County Sligo, reached via the Gleniff Loop road.
- Access and permission: the land is privately owned and grazed. The old route up from the former schoolhouse has been closed off by the landowners since 2015. Admire the cave from the valley floor or the loop road unless you have explicit permission to climb.
- The climb, if you have permission: it’s a relentless scramble of roughly 400 vertical metres straight up from the old school, and the final section relies on old fixed ropes that should never be trusted with your full body weight. In February 2015 a group of students had to be rescued here after icy weather trapped them at the cave. This is not a walk for families, casual hikers, or anyone without solid scrambling experience and proper boots.
- Parking and facilities: there’s a small free parking area at the Gleniff Horseshoe trailhead, and nothing at all up at the cave – carry your own water, food and a map.
- Best time to visit: late spring to early autumn for the most settled weather and longest days. Winter is best avoided, between ice, wind and short daylight.
- Cost: free, open year-round.
Visiting tips
- Check the weather: conditions on the Dartry Mountains change fast; carry waterproofs and layers even on a bright morning.
- Navigation: the Gleniff Horseshoe loop is only partly marked and easy to lose in mist – carry an offline or Ordnance Survey map.
- Leave no trace: this is a working grazing and archaeological site; stay on paths, don’t disturb nesting birds, and take all litter out.
- Mobile coverage: signal is patchy on the cliffs, so tell someone your route and expected return.
Nearby attractions
- Walk the Benbulben Forest Walk for a gentler way onto the mountain’s slopes.
- See the Carrowmore Megalithic Cemetery and the Carrowkeel passage tombs, both a short drive off and among Ireland’s oldest monuments.
- Visit Castlebaldwin for its 15th-century castle and nearby stone circle.
For the clearest views and the best chance of the peregrines, aim for a quiet morning in May or June – and keep your feet on the valley floor.